掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/202348479

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掲載種別：研究論文（学術雑誌）  

We selected sources with a steep soft-X-ray-band spectrum with a photon index of F > 2.5 - measured by eROSITA on board the Spectrum-Röntgen-Gamma (SRG) - from the eFEDS AGN catalogue as candidates of highly accreting supermassive black holes, and investigated their multi-wavelength properties. Among 601 bright AGN with 0.2-5 keV counts of greater than 100, 83 sources (≈14%) are classified as steep-spectrum sources. These sources have typical 0.5-2 keV luminosities of LSX ≈ 1044 erg s-1 and the majority of them are found at redshifts below z = 1. In comparison with sources with flatter spectra, these sources have, on average, a UV (or optical) to 2 keV luminosity ratio that is larger by ~0.3 dex and bluer optical-to-UV continuum emission. They also appear to be radio quiet based on the detection rate in the FIRST and VLASS surveys. Their host galaxies - at least in the redshift range of z = 0.2 - 0.8, where the AGN- galaxy decomposition results from the Subaru Hyper Suprime-Cam imaging are available - tend to be late-type and have smaller stellar masses (M∗ ~ 1010.5~M⊙) than those of sources with flatter spectra. These properties are similar to those found in nearby narrow-line Seyfert 1 galaxies, in agreement with the picture that they are AGN with elevated accretion rates and are in the early growth phase of black hole and galaxy co-evolution. However, the steep-spectrum sources are not exclusively narrow-line Seyfert 1 galaxies; indeed many are broad-line Seyfert 1 galaxies, as found by a catalogue search. This suggests that these steep-spectrum sources may be black holes generally with high accretion rates but of a wide mass range, including a few objects emitting at LSX ≥ 1045 erg s-1, of which black hole masses can be close to 109 M⊙

DOI： 10.1051/0004-6361/202348311

Scopus

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掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/2041-8213/ad35c7

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DOI： 10.21203/rs.3.rs-4005467/v1

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掲載種別：研究論文（学術雑誌）  

We investigate the black hole mass function (BHMF) and Eddington-ratio distribution function (ERDF) of broad-line active galactic nuclei (AGNs) at z = 4, based on a sample of 52 quasars with i < 23.2 at 3.50 ≤ z ≤ 4.25 from the Hyper Suprime-Cam Subaru Strategic Program S16A-Wide2 data set, and 1462 quasars with i < 20.2 in the same redshift range from the Sloan Digital Sky Survey data release 7 quasar catalog. Virial black hole (BH) masses of quasars are estimated using the width of the CIV 1549 Å line and the continuum luminosity at 1350 Å. To obtain the intrinsic broad-line AGN BHMF and ERDF, we correct for the incompleteness in the low-mass and/or low-Eddington-ratio ranges caused by the flux-limited selection. The resulting BHMF is constrained down to log M BH / M ⊙ ∼ 7.5 . In comparison with broad-line AGN BHMFs at z ∼ 2 in the literature, we find that the number density of massive SMBHs peaks at higher redshifts, consistent with the downsizing evolutionary scenario. Additionally, the resulting ERDF shows a negative dependence on BH mass, suggesting more massive SMBHs tend to accrete at lower-Eddington ratios at z = 4. With the derived intrinsic broad-line AGN BHMF, we also evaluate the active fraction of broad-line AGNs among the entire SMBH population at z = 4. The resulting active fraction may suggest a positive dependence on BH mass. Finally, we examine the time evolution of broad-line AGN BHMF between z = 4 and 6 through solving the continuity equation. The results suggest that the broad-line AGN BHMFs at z = 4-6 only show evolution in their normalization, but with no significant changes in their shape.

DOI： 10.3847/1538-4357/ad1518

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Herein, we present the statistical properties of active galactic nuclei
(AGNs) for approximately 1 million member galaxies of galaxy groups and
clusters, with 0.1 $<$ cluster redshift ($z_{\rm cl}$) $<$ 1.4, selected using
Subaru Hyper Suprime-Cam, the so-called CAMIRA clusters. In this research, we
focused on the AGN power fraction ($f_{\rm AGN}$), which is defined as the
proportion of the contribution of AGNs to the total infrared (IR) luminosity,
$L_{\rm IR}$ (AGN)/$L_{\rm IR}$, and examined how $f_{\rm AGN}$ depends on (i)
$z_{\rm cl}$ and (ii) the distance from the cluster center. We compiled
multiwavelength data using the ultraviolet--mid-IR range. Moreover, we
performed spectral energy distribution fits to determine $f_{\rm AGN}$ using
the CIGALE code with the SKIRTOR AGN model. We found that (i) the value of
$f_{\rm AGN}$ in the CAMIRA clusters is positively correlated with $z_{\rm
cl}$, with the correlation slope being steeper than that for field galaxies,
and (ii) $f_{\rm AGN}$ exhibits a high value at the cluster outskirts. These
results indicate that the emergence of AGN population depends on the redshift
and environment and that galaxy groups and clusters at high redshifts are
important in AGN evolution. Additionally, we demonstrated that cluster--cluster
mergers may enhance AGN activity at the outskirts of particularly massive
galaxy clusters. Our findings are consistent with a related study on the CAMIRA
clusters that was based on the AGN number fraction.

DOI： 10.48550/arXiv.2402.11188

arXiv

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その他リンク： http://arxiv.org/pdf/2402.11188v1

掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

Abstract

We  present the demography of the dynamics and gas mass fraction of 33 extremely metal-poor galaxies (EMPGs) with metallicities of 0.015–0.195 Z_⊙ and low stellar masses of 10⁴–10⁸M_⊙ in the local universe. We conduct deep optical integral field spectroscopy (IFS) for the low-mass EMPGs with the medium-high resolution (R = 7500) grism of the 8 m Subaru FOCAS IFU instrument by the EMPRESS 3D survey, and investigate the Hα emission of the EMPGs. Exploiting the resolution high enough for the low-mass galaxies, we derive gas dynamics with the Hα lines by the fitting of three-dimensional disk models. We obtain an average maximum rotation velocity (v_rot) of 15 ± 3 km s⁻¹ and an average intrinsic velocity dispersion (σ₀) of 27 ± 10 km s⁻¹ for 15 spatially resolved EMPGs out of 33 EMPGs, and find that all 15 EMPGs have v_rot/σ₀ &lt; 1 suggesting dispersion-dominated systems. There is a clear decreasing trend of v_rot/σ₀ with the decreasing stellar mass and metallicity. We derive the gas mass fraction (f_gas) for all 33 EMPGs, and find no clear dependence on stellar mass and metallicity. These v_rot/σ₀ and f_gas trends should be compared with young high-z galaxies observed by the forthcoming JWST IFS programs to understand the physical origins of the EMPGs in the local universe.

DOI： 10.3847/1538-4357/ad06ab

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ad06ab/pdf

掲載種別：研究論文（学術雑誌）  

One of the key questions on active galactic nuclei (AGN) in galaxy clusters is how AGN could affect the formation and evolution of member galaxies and galaxy clusters in the history of the Universe. To address this issue, we investigate the dependence of AGN number fraction (fAGN) on cluster redshift (zcl) and distance from the cluster center (RR200). We focus on more than 27000 galaxy groups and clusters at 0.1 < zcl < 1.4 with more than 1 million member galaxies selected from the Subaru Hyper Suprime-Cam. By combining various AGN selection methods based on infrared (IR), radio, and X-ray data, we identify 2688 AGN. We find that (i) fAGN increases with zcl and (ii) fAGN decreases with RR200. The main contributors to the rapid increase of fAGN towards high-z and cluster center are IR- and radio-selected AGN, respectively. These results indicate that the emergence of the AGN population depends on the environment and redshift, and galaxy groups and clusters at high z play an important role in AGN evolution. We also find that cluster-cluster mergers may not drive AGN activity in at least the cluster center, while we have tentative evidence that cluster-cluster mergers could enhance AGN activity in the outskirts of (particularly massive) galaxy clusters.

DOI： 10.1093/pasj/psad066

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press (OUP)  

Abstract

Many massive quiescent galaxies have been discovered at z &amp;gt; 2 thanks to multi-wavelength deep and wide surveys, however, substantial deep near-infrared spectroscopic observations are needed to constrain their star-formation histories statistically. Here, we present a new technique to select quiescent galaxies with a short quenching timescale (≤0.1 Gyr) at z ∼ 2 photometrically. We focus on a spectral break at ∼1600 Å that appears for such fast-quenching galaxies ∼1 Gyr after quenching when early A-type stars go out, but late A-type stars still live. This spectral break at z ∼ 2 is similar to a Lyman break at z ∼ 4. We construct a set of color criteria for z ∼ 2 fast-quenching galaxies on g − r vs. r − i and i − J vs. J − H or $\rm i-[3.6]$ vs. $\rm [3.6]-[4.5]$ color diagrams, which are available with the existing and/or future wide imaging surveys, by simulating various model galaxy spectra and test their robustnesses using the COSMOS2020 catalog. Galaxies with photometric and/or spectroscopic redshifts z ∼ 2 and low specific star formation rates are successfully selected using these colors. The number density of these fast-quenching galaxy candidates at z ∼ 2 suggests that massive galaxies not so far above the star-formation main sequence at z = 3 − 4 should be their progenitors.

DOI： 10.1093/mnras/stad3210

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society (APS)  

DOI： 10.1103/physrevd.108.063510

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.108.063510/fulltext

掲載種別：研究論文（学術雑誌）  

The detection of starlight from the host galaxies of quasars during the reionization epoch (z > 6) has been elusive, even with deep Hubble Space Telescope observations 1,2. The current highest redshift quasar host detected 3, at z = 4.5, required the magnifying effect of a foreground lensing galaxy. Low-luminosity quasars 4–6 from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) 7 mitigate the challenge of detecting their underlying, previously undetected host galaxies. Here we report rest-frame optical images and spectroscopy of two HSC-SSP quasars at z > 6 with the JWST. Using near-infrared camera imaging at 3.6 and 1.5 μm and subtracting the light from the unresolved quasars, we find that the host galaxies are massive (stellar masses of 13 × and 3.4 × 1010 M ☉, respectively), compact and disc-like. Near-infrared spectroscopy at medium resolution shows stellar absorption lines in the more massive quasar, confirming the detection of the host. Velocity-broadened gas in the vicinity of these quasars enables measurements of their black hole masses (1.4 × 109 and 2.0 × 108 M ☉, respectively). Their location in the black hole mass–stellar mass plane is consistent with the distribution at low redshift, suggesting that the relation between black holes and their host galaxies was already in place less than a billion years after the Big Bang.

DOI： 10.1038/s41586-023-06345-5

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PubMed

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

Abstract

We present kinematics of six local extremely metal-poor galaxies (EMPGs) with low metallicities (0.016–0.098 Z_⊙) and low stellar masses (10^4.7–10^7.6M_⊙). Taking deep medium/high-resolution (R ∼ 7500) integral-field spectra with 8.2 m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with Hα emission. Carefully masking out substructures originating by inflow and/or outflow, we fit three-dimensional disk models to the observed Hα flux, velocity, and velocity dispersion maps. All the EMPGs show rotational velocities (v_rot) of 5–23 km s⁻¹ smaller than the velocity dispersions (σ₀) of 17–31 km s⁻¹, indicating dispersion-dominated (v_rot/σ₀ = 0.29–0.80 &lt; 1) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions of f_gas ≃ 0.9–1.0. Comparing our results with other Hα kinematics studies, we find that v_rot/σ₀ decreases and f_gas increases with decreasing metallicity, decreasing stellar mass, and increasing specific star formation rate. We also find that simulated high-z (z ∼ 7) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope observations at z ∼ 7.

DOI： 10.3847/1538-4357/accc87

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/accc87/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

Abstract

We search for local extremely metal-poor galaxies (EMPGs), selecting photometric candidates by broadband color excess and machine-learning techniques with the SDSS photometric data. After removing stellar contaminants by shallow spectroscopy with Seimei and Nayuta telescopes, we confirm that three candidates are EMPGs with 0.05–0.1 Z_⊙ by deep Magellan/MagE spectroscopy for faint [Oiii]λ4363 lines. Using a statistical sample consisting of 105 spectroscopically confirmed EMPGs taken from our study and the literature, we calculate the cross-correlation function (CCF) of the EMPGs and all SDSS galaxies to quantify environments of EMPGs. Comparing another CCF of all SDSS galaxies and comparison of SDSS galaxies in the same stellar-mass range (10^7.0–10^8.4M_⊙), we find no significant (&gt;1σ) difference between these two CCFs. We also compare mass–metallicity relations (MZRs) of the EMPGs and those of galaxies at z ∼ 0–4 with a steady chemical evolution model and find that the EMPG MZR is comparable with the model prediction on average. These clustering and chemical properties of EMPGs are explained by a scenario of stochastic metal-poor gas accretion on metal-rich galaxies showing metal-poor star formation. Extending the broadband color excess technique to a high-z EMPG search, we select 17 candidates of z ∼ 4–5 EMPGs with the deep (≃30 mag) near-infrared JWST/NIRCam images obtained by ERO and ERS programs. We find galaxy candidates with negligible [Oiii]λλ 4959,5007 emission weaker than the local EMPGs and known high-z galaxies, suggesting that some of these candidates may fall in the range of 0–0.01 Z_⊙, which potentially breaks the lowest metallicity limit known to date.

DOI： 10.3847/1538-4357/accf14

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/accf14/pdf

掲載種別：研究論文（学術雑誌）  

We present the quasar luminosity function (LF) at z = 7, measured with 35 spectroscopically confirmed quasars at 6.55 < z < 7.15. The sample of 22 quasars from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, combined with 13 brighter quasars in the literature, covers an unprecedentedly wide range of rest-frame ultraviolet magnitudes over -28 < M 1450 < -23. We found that the binned LF flattens significantly toward the faint end populated by the SHELLQs quasars. A maximum likelihood fit to a double power-law model has a break magnitude M1450∗=-25.60-0.30+0.40, a characteristic density φ∗=1.35-0.30+0.47 Gpc-3 mag-1, and a bright-end slope β=-3.34-0.57+0.49, when the faint-end slope is fixed to α = -1.2 as observed at z ≤ 6. The overall LF shape remains remarkably similar from z = 4 to 7, while the amplitude decreases substantially toward higher redshifts, with a clear indication of an accelerating decline at z ≥ 6. The estimated ionizing photon density, 1048.2±0.1 s-1 Mpc-3, is less than 1% of the critical rate to keep the intergalactic medium ionized at z = 7, and thus indicates that quasars are not a major contributor to cosmic reionization.

DOI： 10.3847/2041-8213/acd69f

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掲載種別：研究論文（学術雑誌）  

Which galaxies in the general population turn into active galactic nuclei (AGNs) is a keystone of galaxy formation and evolution. Thanks to SRG/eROSITA- s contiguous 140 square degree pilot survey field, we constructed a large, complete, and unbiased soft X-ray flux-limited (FX > 6.5 × 10-15 erg s-1 cm-2) AGN sample at low redshift, 0.05 < z < 0.55. Two summary statistics, the clustering using spectra from SDSS-V and galaxy-galaxy lensing with imaging from HSC, are measured and interpreted with halo occupation distribution and abundance matching models. Both models successfully account for the observations. We obtain an exceptionally complete view of the AGN halo occupation distribution. The population of AGNs is broadly distributed among halos with a mean mass of 3.9-2.4+2.0 × 1012 Mo. This corresponds to a large-scale halo bias of b(z = 0.34) = 0.99-0.10+0.08. The central occupation has a large transition parameter, slog10(M) = 1.28 ± 0.2. The satellite occupation distribution is characterized by a shallow slope, asat = 0.73 ± 0.38. We find that AGNs in satellites are rare, with fsat < 20%. Most soft X-ray-selected AGNs are hosted by central galaxies in their dark matter halo. A weak correlation between soft X-ray luminosity and large-scale halo bias is confirmed (3.3s). We discuss the implications of environmental-dependent AGN triggering. This study paves the way toward fully charting, in the coming decade, the coevolution of X-ray AGNs, their host galaxies, and dark matter halos by combining eROSITA with SDSS-V, 4MOST, DESI, LSST, and Euclid data.

DOI： 10.1051/0004-6361/202245726

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

yWe constructed the eROSITA X-ray catalog of radio galaxies discovered by the WERGS survey, made by cross-matching the wide area Subaru/Hyper Suprime-Cam (HSC) optical survey and VLA/FIRST 1.4 GHz radio survey. We report finding 393 eROSITA detected radio galaxies in the 0.5 2 keV band in the eFEDS field covering 140 deg(2). Thanks to the wide and medium depth eFEDS X-ray survey down to f(0.5-2 keV) = 6 :5 x10-(15) erg s(-1) cm(-2), the sample contains the rare and most X-ray luminous radio galaxies above the knee of the X-ray luminosity function, spanning 44 < log(L0.5-2keV ((abs,corr)) /ergs(-1)) < 46:5 at 1 < z < 4. The sample also contains the sources around and below the knee for the sources 41 < log(L0.5-2keV((abs,corr)) /ergs(-1) < 45 at z < 1. Based on the X-ray properties obtained by the spectral fitting, 37 sources show obscured active galactic nucleus (AGN) signatures with log(N-H =cm(-2)) > 22. These obscured and radio AGN reside in 0:4 < z < 3:2, indicating that they are obscured counterparts of the radio-loud quasar, which were missed in the previous optical quasar surveys. By combining radio and X-ray luminosities, we also investigated the jet production efficiency eta(jet) = eta P-rad(jet) / L-AGN;bol by utilizing the jet power of P-jet. We find that there are 14 sources with extremely high jet production efficiency at eta(jet) approximate to 1. This high eta(jet) value might be a result of the decreased radiation efficiency of eta(rad) < 0:1, due to the low accretion rate for those sources, and /or of the boosting due to the decline of LAGN;bol by a factor of 10 100 by keeping Pjet constant in the previous Myr, indicating the experience of the AGN feedback. Finally, inferring the BH masses from the stellar mass, we find that X-ray luminous sources show the excess of the radio emission with respect to the value estimated from the fundamental plane. This radio emission excess cannot be explained by the Doppler boosting alone, and therefore the disk-jet connection of X-ray luminous eFEDS-WERGS is fundamentally different from the conventional fundamental plane which mainly covers the low-accretion regime.

DOI： 10.1051/0004-6361/202244271

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP Publishing Ltd  

We present Karl G. Jansky Very Large Array K-band (19 GHz) observations of the redshifted CO(1-0) line emission toward the radio galaxy TN J0924-2201 at z = 5.2, which is one of the most distant radio galaxies with CO detected. With an angular resolution of similar to 2 '', the CO(1-0) line emission is resolved into three clumps, within +/- 500 km s(-1) relative to its redshift, which is determined by Ly alpha. We find that the clumps are located off-center and 12-33 kpc away from the center of the host galaxy, which has counterparts in the Hubble Space Telescope i band, Spitzer/IRAC, and the Atacama Large Millimeter/submillimeter Array (ALMA) band 6 (230 GHz; 1.3 mm). With the ALMA detection, we estimate the infrared luminosity LIR and the star formation rate (SFR) of the host galaxy to be (9.3 +/- 1.7) x 10(11)L(circle dot) and 110 +/- 20 M-circle dot yr(-1), respectively. We also derive the 3 sigma upper limit of M-H2 < 1.3 x 10(10) M-circle dot at the host galaxy. The 2 detected CO(1-0) line luminosities of the three clumps, L '(CO (1-0)) = (3.2-4.7) x 10(10) K km s(-1) pc(2), indicate the presence of three massive molecular gas reservoirs, with M-H2 = (2.5-3.7) x 10(10) M-circle dot, assuming a CO-to-H-2 conversion factor of alpha(CO) = 0.8 M-circle dot (K km s(-1) pc(2))(-1), although the SFR is not elevated due to the nondetection of the ALMA -1.3 mm continuum (SFR < 40 M-circle dot yr(-1)). From the host galaxy, the nearest molecular gas clump, labeled "clump A," is apparently in alignment with the radio jet axis, showing radio-CO alignment. The origins of these three clumps around TN J0924-2201 can possibly be interpreted as outflows, mergers, or jet-induced metal enrichment.

DOI： 10.3847/1538-4357/acaf58

Web of Science

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psac073

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psac075

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/202243502

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stac2681

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その他リンク： https://academic.oup.com/mnras/article-pdf/517/1/1264/46441587/stac2681.pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4365/ac7710

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4365/ac7710/pdf

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPIE  

DOI： 10.1117/12.2627749

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac7f2d

Scopus

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac7f2d/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac77ee

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac77ee/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psac018

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/202141631

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/202141547

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/202141092

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac5b71

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac5b71/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4365/ac3d31

Scopus

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4365/ac3d31/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac441c

Web of Science

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac441c/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac3509

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac3509/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/202142059

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac2301

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac2301/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac1b26

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac1b26/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac1ff0

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac1ff0/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/202039376

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac06a8

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac06a8/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac0f07

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac0f07/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac1106

Scopus

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac1106/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psab065

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ac0adf

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ac0adf/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abf6dc

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/abf6dc/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abe7ea

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/abe7ea/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abe94a

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/abe94a/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abec3d

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/abec3d/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/202140317

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abea15

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/abea15/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1017/pasa.2021.13

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/abd7ef

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/abd7ef/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

DOI： 10.3847/1538-4357/abbe11

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/abbe11

掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press (OUP)  

<title>Abstract</title>
To determine the dominant sources for cosmic reionization, the evolution history of the global ionizing fraction, and the topology of the ionized regions, we have conducted a deep imaging survey using four narrow-band (NB) and one intermediate-band (IB) filters on the Subaru/Hyper Suprime-Cam (HSC), called Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS). The central wavelengths and full-widths-at-half-maximum of the CHORUS filters are, respectively, 386.2 nm and 5.5 nm for NB387, 526.0 nm and 7.9 nm for NB527, 717.1 nm and 11.1 nm for NB718, 946.2 nm and 33.0 nm for IB945, and 971.2 nm and 11.2 nm for NB973. This combination, including NB921 (921.5 nm and 13.5 nm) from the Subaru Strategic Program with HSC (HSC SSP), is carefully designed, as if they were playing a chorus, to observe multiple spectral features simultaneously, such as Lyman continuum, Lyα, C iv, and He ii for $z$ = 2–7. The observing field is the same as that of the deepest footprint of the HSC SSP in the COSMOS field and its effective area is about 1.6 deg2. We present an overview of the CHORUS project, which includes descriptions of the filter design philosophy, observations and data reduction, multiband photometric catalogs, assessments of the imaging quality, measurements of the number counts, and example use cases for the data. All the imaging data, photometric catalogs, masked pixel images, data of limiting magnitudes and point spread functions, results of completeness simulations, and source number counts are publicly available through the HSC SSP database.

DOI： 10.1093/pasj/psaa100

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press (OUP)  

<title>Abstract</title>
Active galactic nuclei (AGNs) are key in understanding the coevolution of galaxies and supermassive black holes (SMBHs). AGN activity is thought to affect the properties of their host galaxies via a process called “AGN feedback,” which drives the coevolution. From a parent sample of 1151 z &amp;lt; 1 type-1 quasars from the Sloan Digital Sky Survey quasar catalog, we detected the host galaxies of 862 of them in the high-quality grizy images of the Subaru Hyper Suprime-Cam survey. The unprecedented combination of the survey area and depth allowed us to perform a statistical analysis of the quasar host galaxies, with small sample variance. We fitted the radial image profile of each quasar as a linear combination of the point spread function and the Sérsic function, decomposing the images into the quasar nucleus and the host galaxy components. We found that the host galaxies are massive, with stellar mass Mstar ≳ 1010 $M_\odot$, and are mainly located on the green valley. This trend is consistent with a scenario in which star formation in the host galaxies is suppressed by AGN feedback, that is, AGN activity may be responsible for the transition of these galaxies from the blue cloud to the red sequence. We also investigated the SMBH mass to stellar mass relation of the z &amp;lt; 1 quasars, and found a consistent slope with the local relation, while the SMBHs may be slightly undermassive. However, the above results are subject to our sample selection, which biases against host galaxies with low masses and/or large quasar-to-host flux ratios.

DOI： 10.1093/pasj/psaa072

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press (OUP)  

<title>Abstract</title>
We present the first discovery of dust-reddened quasars (red quasars) in the high-z universe (z &amp;gt; 5.6). This is a result from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which is based on the sensitive multi-band optical imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. We identified four red quasar candidates from the 93 spectroscopically confirmed high-z quasars in the SHELLQs sample, based on detections in the Wide-field Infrared Survey Explorer (WISE) data at 3.4 and 4.6 μm (rest-frame ∼5000–6500 Å). The amount of dust reddening was estimated with spectral energy distribution (SED) fits over optical and mid-infrared wavelengths. Two of the four candidates were found to be red quasars with dust reddening of E(B − V) &amp;gt; 0.1. The remaining SHELLQs quasars without individual WISE detections are significantly fainter in the WISE bands and bluer than the red quasars, although we did detect them in the W1 band in a stacked image. We also conducted the same SED fits for high-z optically-luminous quasars, but no red quasar was found. This demonstrates the power of Subaru HSC to discover high-z red quasars, which are fainter than the limiting magnitudes of past surveys in the rest-frame ultraviolet, due to dust extinction.

DOI： 10.1093/pasj/psaa074

Web of Science

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

DOI： 10.3847/1538-4357/aba4a3

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/aba4a3

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

DOI： 10.3847/1538-4357/aba047

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/aba047

記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

DOI： 10.3847/1538-4357/aba193

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/aba193

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

DOI： 10.3847/1538-4357/ab99a8

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ab99a8

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

DOI： 10.3847/1538-4357/ab9b7f

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ab9b7f

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

DOI： 10.3847/1538-3881/ab98fe

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-3881/ab98fe

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

DOI： 10.3847/1538-4357/ab94bd

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その他リンク： https://iopscience.iop.org/article/10.3847/1538-4357/ab94bd

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psaa004

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab7917

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2019. The American Astronomical Society. All rights reserved. We report the discovery of a Compton-thick (CT), dust-obscured galaxy at z = 0.89, WISE J082501.48+300257.2 (WISE 0825+3002), observed by the Nuclear Spectroscopic Telescope Array. X-ray analysis with the XCLUMPY model revealed that hard X-ray luminosity in the rest-frame 2-10 keV band of WISE 0825+3002 is L X (2-10 keV) = erg s-1 while its hydrogen column density is N H = cm-2 indicating that WISE 0825+3002 is a mildly CT active galactic nucleus (AGN). We performed spectral energy distribution (SED) fitting with CIGALE to derive its stellar mass, star formation rate, and infrared luminosity. The estimated Eddington ratio based on stellar mass and integration of the best-fit SED of the AGN component is λ Edd = 0.70, which suggests that WISE 0825+3002 harbors an actively growing black hole behind a large amount of gas and dust. We found that the relationship between the luminosity ratio of X-ray and 6 μm, and Eddington ratio, follows an empirical relation for AGNs reported by Toba et al.

DOI： 10.3847/1538-4357/ab5718

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psz096

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stz2522

Web of Science

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/stz2034

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/2041-8213/ab412e

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Astronomical Society  

DOI： 10.3847/2515-5172/ab3228

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その他リンク： https://iopscience.iop.org/article/10.3847/2515-5172/ab3228

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Cambridge University Press (CUP)  

<title>Abstract</title>We present ALMA [CII] line and far-infrared (FIR) continuum observations of seven <italic>z</italic> &gt; 6 low-luminosity quasars (<italic>M</italic>₁₄₅₀ &gt; −25 mag) discovered by our on-going Subaru Hyper Suprime-Cam survey. The [CII] line was detected in all targets with luminosities of ∼(2−10) × 10⁸ L_⊙, about one order of magnitude smaller than optically luminous quasars. Also found was a wide scatter of FIR continuum luminosity, ranging from <italic>L</italic>_FIR &lt; 10¹¹<italic>L</italic>_⊙ to ∼2 × 10¹²<italic>L</italic>_⊙. With the [CII]-based dynamical mass, we suggest that a significant fraction of low-luminosity quasars are located on or even below the local Magorrian relation, particularly at the massive end of the galaxy mass distribution. This is a clear contrast to the previous finding that luminous quasars tend to have overmassive black holes relative to the relation. Our result is expected to show a less-biased nature of the early co-evolution of black holes and their host galaxies.

DOI： 10.1017/s1743921319009487

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab0d22

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/ab1415

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Cambridge University Press  

We report the first detection of [NII] 122 μm line toward a QSO-SMG pair, BRI 1202-0725, at z = 4.7 using ALMA. Combining with [NII] 205 μm line detection and taking the line ratio of [NII]122/[NII]205, we constrain electron densities of both galaxies. The derived electron densities are and cm-3 for the SMG and the QSO, respectively, which are the first measurements for galaxies at z &gt
4. The electron density of the SMG is comparable to the Galactic plane and the average of local spiral galaxies, while the value for the QSO is comparable to local starbursts and optical-line based measurements for star-forming galaxies at z ∼ 2-3. Considering the similar star-formation rates (SFRs) of 1000 M yr-1 for both galaxies, our results suggest a large scatter of electron densities at fixed SFR and caution against using optical lines for dusty starbursts. The details of this report are presented in Lee et al. 2019 (submitted).

DOI： 10.1017/S1743921319004782

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Cambridge University Press  

We present the physical properties of Lyα emitters (LAEs) in a DLA-concentrated regions where there are 3 or more DLA within (50 Mpc)3 cubic box. We observed LAEs in a DLA-concentrated region at z = 2.3, the J1230+34 field, with Subaru/Suprime-Cam. In the 50 Mpc scale, we found no deferences in properties of LAEs such as Lyα luminosity function in the DLA-concentrated region compared to other fields at similar redshift. On the other hand, we found a ∼10 Mpc scale LAE overdensity around a strong DLA with NHI = 1021.08 cm-2.

DOI： 10.1017/S1743921319001388

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnrasl/sly167

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/mnras/sty1394

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aac6c4

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

We investigate Lyα, [O iii] λ5007, Hα, and [C ii] 158 μm emission from 1124 galaxies at z = 4.9-7.0. Our sample is composed of 1092 Lyα emitters (LAEs) at z = 4.9, 5.7, 6.6, and 7.0 identified by Subaru/Hyper-Suprime-Cam (HSC) narrowband surveys covered by Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) and 34 galaxies at z = 5.148-7.508 with deep ALMA [C ii] 158 μm data in the literature. Fluxes of strong rest-frame optical lines of [O iii] and Hα (Hβ) are constrained by significant excesses found in the SPLASH 3.6 and 4.5 μm photometry. At z = 4.9, we find that the rest-frame Hα equivalent width and the Lyα escape fraction f Lyα positively correlate with the rest-frame Lyα equivalent width fLyα positively correlate with the rest-frame Lyα equivalent width EWLyα0 . The correlation is similarly found at z ∼ 0-2, suggesting no evolution of the correlation over z ≃ 0-5. The typical ionizing photon production efficiency of LAEs is log(ξ ion/[Hz erg-1]) ≃ 25.5, significantly (60%-100%) higher than those of LBGs at a given UV magnitude. At z = 5.7-7.0, there exists an interesting turnover trend that the [O iii]/Hα flux ratio increases in and then decreases out to . We also identify an anticorrelation between a ratio of [C ii] luminosity to star formation rate (L [C ii]/SFR) and at the &gt
99% confidence level.. We carefully investigate physical origins of the correlations with stellar-synthesis and photoionization models and find that a simple anticorrelation between and metallicity explains self-consistently all of the correlations of Lyα, Hα, [O iii]/Hα, and [C ii] identified in our study, indicating detections of metal-poor (∼0.03 Z o) galaxies with .

DOI： 10.3847/1538-4357/aabd80

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psy026

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

We present the discovery of an extremely luminous dust-obscured galaxy (DOG) at z spec = 3.703, WISE J101326.25+611220.1. This DOG is selected as a candidate of extremely luminous infrared (IR) galaxies based on the photometry from the Sloan Digital Sky Survey and Wide-field Infrared Survey Explorer. In order to derive its accurate IR luminosity, we perform follow-up observations at 450 and 850 μm using the Submillimetre Common User Bolometer Array 2 on the James Clerk Maxwell Telescope, and at 870 and 1300 μm using the Submillimeter Array, which enable us to pin down its IR Spectral Energy Distribution (SED). We perform SED fitting using 14 photometric data (0.4-1300 μm) and estimate its IR luminosity, L IR (8-1000 μm), to be × 1014 L, making it one of the most luminous IR galaxies in the universe. The energy contribution from an active galactic nucleus (AGN) to the IR luminosity is %, which indicates that it is an AGN-dominated DOG. On the other hand, its stellar mass (M ∗) and star formation rate (SFR) are = and ) =, respectively, which means that this DOG can be considered a starburst galaxy in the M ∗-SFR plane. This extremely luminous DOG shows significant AGN and star-forming activity that provides us with an important laboratory to probe the maximum phase of the coevolution of galaxies and supermassive black holes.

DOI： 10.3847/1538-4357/aab3cf

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

While major mergers have long been proposed as a driver of both active galactic nucleus (AGN) activity and theMBH-sbulge relation, studies of moderate to high-redshift Seyfert-luminosity AGN hosts have found little evidencefor enhanced rates of interactions. However, both theory and observation suggest that while these AGNs may befueled by stochastic accretion and secular processes, high-luminosity, high-redshift, and heavily obscured AGNsare the AGNs most likely to be merger-driven. To better sample this population of AGNs, we turn to infraredselection in the CANDELS/COSMOS field. Compared to their lower-luminosity and less obscured X-ray-onlycounterparts, IR-only AGNs (luminous, heavily obscured AGNs) are more likely to be classified as either irregular(50-12+12 versus 9 % 25-+ ) or asymmetric (69 % 139-+ versus 17 % 46-+ ) and are less likely to have a spheroidal component(31 9 %13-+ versus 77 % 64-+ ). Furthermore, IR-only AGNs are also significantly more likely than X-ray-only AGNs(75 13%8-+ versus 31 % 66-+ ) to be classified either as interacting or merging in a way that significantly disturbs the hostgalaxy or as disturbed, though not clearly interacting or merging, which potentially represents the late stages of amajor merger. This suggests that while major mergers may not contribute significantly to the fueling of SeyfertluminosityAGNs, interactions appear to play a more dominant role in the triggering and fueling of high-luminosityheavily obscured AGNs.

DOI： 10.3847/1538-4357/aa9ffa

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We conduct a systematic search for galaxy protoclusters at z ∼ 3.8 based on the latest internal data release (S16A) of the Hyper Suprime-Cam Subaru strategic program (HSCSSP). In the Wide layer of the HSC-SSP, we investigate the large-scale projected sky distribution of g-dropout galaxies over an area of 121 deg2, and identify 216 large-scale overdense regions (&gt
4 σ overdensity significance) that are likely protocluster candidates. Of these, 37 are located within 8 (3.4 physical Mpc) of other protocluster candidates of higher overdensity, and are expected to merge into a single massive structure by z = 0. Therefore, we find 179 unique protocluster candidates in our survey. A cosmological simulation that includes projection effects predicts that more than 76% of these candidates will evolve into galaxy clusters with halo masses of at least 1014 M by z = 0. The unprecedented size of our protocluster candidate catalog allows us to perform, for the first time, an angular clustering analysis of the systematic sample of protocluster candidates. We find a correlation length of 35.0 h-1 Mpc. The relation between correlation length and number density of z ∼ 3.8 protocluster candidates is consistent with the prediction of the ΣCDM model, and the correlation length is similar to that of rich clusters in the local universe. This result suggests that our protocluster candidates are tracing similar spatial structures to those expected from the progenitors of rich clusters, and enhances the confidence that our method for identifying protoclusters at high redshifts is robust. In years to come, our protocluster search will be extended to the entire HSC-SSP Wide sky coverage of ∼1400 deg2 to probe cluster formation over a wide redshift range of z ∼ 2-6.

DOI： 10.1093/pasj/psx102

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We investigate the galaxy overdensity around proto-cluster scale quasar pairs at high (z &gt
3) and low (z ∼ 1) redshift based on the unprecedentedly wide and deep optical survey of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using the firstyear survey data covering effectively ∼121 deg2 with the 5σ depth of i ∼ 26.4 and the SDSS DR12Q catalog, we find two luminous pairs at z ∼ 3.3 and 3.6 which reside in &gt
5σ overdensity regions of g-dropout galaxies at i &lt
25. The projected separations of the two pairs are R = 1.75 and 1.04 proper Mpc (pMpc), and their velocity offsets are ΔV = 692 and 1448kms-1, respectively. This result is in clear contrast to the average z ∼ 4 quasar environments as discussed in Uchiyama et al. (2018, PASJ 70, S32) and implies that the quasar activities of the pair members are triggered via major mergers in proto-clusters, unlike the vast majority of isolated quasars in general fields that may turn on via non-merger events such as bar and disk instabilities. At z ∼ 1, we find 37 pairs with R &lt
2pMpc and ΔV &lt
2300kms-1 in the current HSC-Wide coverage, including four from Hennawi et al. (2006, AJ, 131, 1). The distribution of the peak overdensity significance within two arcminutes around the pairs has a long tail toward high-density (&gt
4σ) regions. Thanks to the large sample size, we find statistical evidence that this excess is unique to the pair environments when compared to single-quasar and randomly selected galaxy environments at the same redshift range.Moreover, there are nine smallscale (R &lt
1 pMpc) pairs, two of which are found to reside in cluster fields. Our results demonstrate that &lt
2 pMpc scale quasar pairs at both redshift ranges tend to occur in massive haloes, although perhaps not the most massive ones, and that they are useful in searching for rare density peaks.

DOI： 10.1093/pasj/psx092

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We present the luminosity function of z ∼ 4 quasars based on the Hyper Suprime-Cam Subaru Strategic Program Wide layer imaging data in the g, r, i, z, and y bands covering 339.8 deg2. From stellar objects, 1666 z ∼ 4 quasar candidates are selected via the g-dropout selection down to i = 24.0mag. Their photometric redshifts cover the redshift range between 3.6 and 4.3, with an average of 3.9. In combination with the quasar sample from the Sloan Digital Sky Survey in the same redshift range, a quasar luminosity function covering the wide luminosity range of M1450 = -22 to -29mag is constructed. The quasar luminosity function is well described by a double power-law model with a knee at M1450 = -25.36±0.13mag and a flat faint-end slope with a power-law index of -1.30±0.05. The knee and faint-end slope show no clear evidence of redshift evolution from those seen at z ∼ 2. The flat slope implies that the UV luminosity density of the quasar population is dominated by the quasars around the knee, and does not support the steeper faint-end slope at higher redshifts reported at z &gt
5. If we convert the M1450 luminosity function to the hard X-ray 2-10 keV luminosity function using the relation between the UV and X-ray luminosity of quasars and its scatter, the number density of UV-selected quasars matches well with that of the X-ray-selected active galactic nuclei (AGNs) above the knee of the luminosity function. Below the knee, the UV-selected quasars show a deficiency compared to the hard X-ray luminosity function. The deficiency can be explained by the lack of obscured AGNs among the UV-selected quasars.

DOI： 10.1093/pasj/psx091

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We study the UV luminosity functions (LFs) at z ∼ 4, 5, 6, and 7 based on the deep largearea optical images taken by the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP). On the 100 deg2 sky of the HSC SSP data available to date, we take enormous samples consisting of a total of 579565 dropout candidates at z ∼ 4-7 by the standard color selection technique, 358 out of which are spectroscopically confirmed by our followup spectroscopy and other studies. We obtain UV LFs at z ∼ 4-7 that span a very wide UV luminosity range of ∼0.002-100 L∗UV (-26 &lt
MUV &lt
-14 mag) by combining LFs from our program and the ultra-deep Hubble Space Telescope legacy surveys.We derive three parameters of the best-fit Schechter function, φ∗, M∗ UV, and α, of the UV LFs in the magnitude range where the active galactic nucleus (AGN) contribution is negligible, and find that α and φ∗ decrease from z ∼ 4 to 7 with no significant evolution of M∗UV. Because our HSC SSP data bridge the LFs of galaxies and AGNs with great statistical accuracy, we carefully investigate the bright end of the galaxy UV LFs that are estimated by the subtraction of the AGN contribution either aided by spectroscopy or the best-fit AGN UV LFs.We find that the bright end of the galaxy UV LFs cannot be explained by the Schechter function fits at&gt
2 σ significance, and require either double power-law functions or modified Schechter functions that consider a magnification bias due to gravitational lensing.

DOI： 10.1093/pasj/psx103

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We have measured the clustering of galaxies around active galactic nuclei (AGNs) for which single-epoch virialmasses of the super-massive black hole (SMBH) are available to investigate the relation between the large-scale environment of AGNs and the evolution of SMBHs. The AGN samples used in this work were derived from the Sloan Digital Sky Survey (SDSS) observations and the galaxy samples were from the 240 deg2 S15b data of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). The investigated redshift range is 0.6-3.0, and the masses of the SMBHs lie in the range 107.5-1010 M. The absolute magnitude of the galaxy samples reaches to Mλ310 ∼ -18 at rest-frame wavelength 310nmfor the low-redshift end of the samples. More than 70% of the galaxies in the analysis are blue.We found a significant dependence of the cross-correlation length on redshift, which primarily reflects the brightness-dependence of the galaxy clustering. At the lowest redshifts the cross-correlation length increases from 7 h-1 Mpc around Mλ310 =-19mag to &gt
10 h-1 Mpc beyond Mλ310 =-20 mag. No significant dependence of the cross-correlation length on BH mass was found for whole galaxy samples dominated by blue galaxies, while there was an indication of BH mass dependence in the crosscorrelation with red galaxies. These results provides a picture of the environment of AGNs studied in this paper being enriched with blue star-forming galaxies, and a fraction of the galaxies are evolving into red galaxies along with the evolution of SMBHs in that system.

DOI： 10.1093/pasj/psx099

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We present initial results from the Subaru Strategic Program (SSP) with Hyper Suprime- Cam (HSC) on a comprehensive survey of emission-line galaxies at z &lt
1.5 based on narrowband imaging. The first Public Data Release provides us with data from two narrowband filters, specifically NB816 and NB921 over 5.7 deg2 and 16.2 deg2 respectively. The 5 σ limiting magnitudes are 25.2mag (UltraDeep layer, 1.4 deg2) and 24.8mag (Deep layer, 4.3 deg2) for NB816, and 25.1mag (UltraDeep, 2.9 deg2) and 24.6-24.8mag (Deep, 13.3 deg2) for NB921. The wide-field imaging allows us to construct unprecedentedly large samples of 8054 Hα emitters at z ≈ 0.25 and 0.40, 8656 [O III] emitters at z ≈ 0.63 and 0.84, and 16877 [O II] emitters at z ≈ 1.19 and 1.47.We map the cosmic web on scales out to about 50 comoving Mpc that includes galaxy clusters, identified by red sequence galaxies, located at the intersection of filamentary structures of star-forming galaxies. The luminosity functions of emission-line galaxies are measured with precision and are consistent with published studies. The wide field coverage of the data enables us to measure the luminosity functions up to brighter luminosities than previous studies. The comparison of the luminosity functions between the different HSC-SSP fields suggests that a survey volume of &gt
5 × 105 Mpc3 is essential to overcome cosmic variance. Since the current data have not reached the full depth expected for the HSC-SSP, the color cut in i - NB816 or z - NB921 induces a bias towards star-forming galaxies with large equivalent widths, primarily seen in the stellar mass functions for the Hα emitters at z ≈ 0.25-0.40. Even so, the emission-line galaxies clearly cover a wide range of luminosity, stellar mass, and environment, thus demonstrating the usefulness of the narrowband data from the HSC-SSP for investigating star-forming galaxies at z &lt
1.5.

DOI： 10.1093/pasj/psx088

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We present an unprecedentedly large catalog consisting of 2230 ≳ L∗ Lyα emitters (LAEs) at z = 5.7 and 6.6 on the 13.8 and 21.2 deg2 sky, respectively, that are identified by the SILVERRUSH program with the first narrow-band imaging data of the Hyper Suprime- Cam (HSC) survey. We confirm that the LAE catalog is reliable on the basis of 96 LAEs whose spectroscopic redshifts are already determined by this program and previous studies. This catalogue is also available online. Based on this catalogue, we derive the rest-frame Lyα equivalent-width distributions of LAEs at z - 5.7-6.6 that are reasonably explained by the exponential profiles with scale lengths of - 120-170A, showing no significant evolution from z - 5.7 to z - 6.6. We find that 275 LAEs with large equivalent widths (LEWs) of &gt
240 A are candidates of young metal poor galaxies and AGNs. We also find that the fraction of LEW LAEs to all LAEs is 4% and 21% at z - 5.7 and z - 6.6, respectively. Our LAE catalog includes 11 Lyα blobs (LABs) that are LAEs with spatially extended Lyα emission with a profile that is clearly distinguished from those of stellar objects at the ≳3σ level. The number density of the LABs at z = 6-7 is ∼10-7-10-6 Mpc-3, being ∼10-100 times lower than those claimed for LABs at z - 2-3, suggestive of disappearing LABs at z ≳ 6, albeit with the different selection methods and criteria for the low and high-z LABs.

DOI： 10.1093/pasj/psx122

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We present Lyα and UV-nebular emission line properties of bright Lyα emitters (LAEs) at z = 6-7 with a luminosity of log LLyα/[erg s-1] = 43-44 identified in the 21 deg2 area of the SILVERRUSH early sample developed with the Subaru Hyper Suprime-Cam survey data. Our optical spectroscopy newly confirms 21 bright LAEs with clear Lyα emission, and contributes to making a spectroscopic sample of 96 LAEs at z = 6-7 in SILVERRUSH. From the spectroscopic sample, we select seven remarkable LAEs as bright as Himiko and CR7 objects, and perform deep Keck/MOSFIRE and Subaru/nuMOIRCS near-infrared spectroscopy reaching the 3 σ flux limit of ∼2 × 10-18 erg s-1 for the UV-nebular emission lines of He II λ1640, CIV λλ1548,1550, and OIII]λλ1661,1666. Except for one tentative detection of C IV, we find no strong UV-nebular lines down to the flux limit, placing the upper limits of the rest-frame equivalent widths (EW0) of ∼2-4 A for CIV, He II, and OIII] lines. We also investigate the VLT/X-SHOOTER spectrum of CR7 whose 6 σ detection of He II is claimed by Sobral et al. Although two individuals and the ESO archive service carefully reanalyzed the X-SHOOTER data that are used in the study of Sobral et al., no He II signal of CR7 is detected, supportive of weak UV-nebular lines of the bright LAEs even for CR7. The spectral properties of these bright LAEs are thus clearly different from those of faint dropouts at z ∼ 7 that have strong UV-nebular lines shown in the various studies. Comparing these bright LAEs and the faint dropouts, we find anti-correlations between the UV-nebular line EW0 and the UV-continuum luminosity, which are similar to those found at z ∼ 2-3.

DOI： 10.1093/pasj/psx107

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We examine the clustering of quasars over a wide luminosity range, by utilizing 901 quasars at zphot ∼ 3.8 with -24.73 &lt
M1450 &lt
-22.23 photometrically selected from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) S16A Wide2 date release and 342 more luminous quasars at 3.4 &lt
zspec &lt
4.6 with -28.0 &lt
M1450 &lt
-23.95 from the Sloan Digital Sky Survey that fall in the HSC survey fields. We measure the bias factors of two quasar samples by evaluating the cross-correlation functions (CCFs) between the quasar samples and 25790 bright z ∼ 4 Lyman break galaxies in M1450 &lt
-21.25 photometrically selected from the HSC dataset. Over an angular scale of 10.0 to 1000.0, the bias factors are 5.93+1.34 -1.43 and 2.73+2.44 -2.55 for the low- and high-luminosity quasars, respectively, indicating no significant luminosity dependence of quasar clustering at z ∼ 4. It is noted that the bias factor of the luminous quasars estimated by the CCF is smaller than that estimated by the auto-correlation function over a similar redshift range, especially on scales below 40.0. Moreover, the bias factor of the less-luminous quasars implies the minimal mass of their host dark matter halos is 0.3-2 × 1012 h-1M, corresponding to a quasar duty cycle of 0.001-0.06.

DOI： 10.1093/pasj/psx129

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psx081

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We present the SILVERRUSH program strategy and clustering properties investigated with ∼2000 Lyα emitters (LAEs) at z = 5.7 and 6.6 found in the early data of the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey exploiting the carefully designed narrow-band filters. We derive angular correlation functions with the unprecedentedly large samples of LAEs at z = 6-7 over the large total area of 14-21 deg2 corresponding to 0.3-0.5 comoving Gpc2. We obtain the average large-scale bias values of bavg = 4.1±0.2 (4.5±0.6) at z = 5.7 (z = 6.6) for L∗ LAEs, indicating a weak evolution of LAE clustering from z = 5.7 to 6.6. We compare the LAE clustering results with two independent theoretical models that suggest an increase of an LAE clustering signal by the patchy ionized bubbles at the epoch of reionization (EoR), and estimate the neutral hydrogen fraction to be xHI = 0.15-0.15+0.15 at z = 6.6. Based on the halo occupation distributionmodels, we find that the L∗ LAEs are hosted by dark-matter halos with an average mass of log(Mh/M) = 11.1-0.4+0.2 (10.8-0.5+0.3) at z = 5.7 (6.6) with a Lyα duty cycle of 1% or less, where the results of z = 6.6 LAEs may be slightly biased, due to the increase of the clustering signal at the EoR. Our clustering analysis reveals the low-mass nature of L∗ LAEs at z = 6-7, and that these LAEs probably evolve into massive super-L∗ galaxies in the present-day universe.

DOI： 10.1093/pasj/psx074

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psx066

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We present the cross-correlation between 151 luminous quasars (MUV &lt
-26) and 179 protocluster candidates at z ∼ 3.8, extracted from the Wide imaging survey (∼121 deg2) performed as part of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We find that only two out of 151 quasars reside in regions that are more overdense compared to the average field at &gt
4 σ. The distributions of the distances between quasars and the nearest protoclusters and the significance of the overdensity at the positions of quasars are statistically identical to those found for g-dropout galaxies, suggesting that quasars tend to reside in almost the same environment as star-forming galaxies at this redshift. Using stacking analysis, we find that the average density of g-dropout galaxies around quasars is slightly higher than that around g-dropout galaxies on 1.0-2.5 pMpc scales, while at &lt
0.5 pMpc that around quasars tends to be lower. We also find that quasars with higher UV luminosity or with more massive black holes tend to avoid the most overdense regions, and that the quasar near-zone sizes are anti-correlated with overdensity. These findings are consistent with a scenario in which luminous quasars at z ∼ 4 reside in structures that are less massive than those expected for the progenitors of today's rich clusters of galaxies, and possibly that luminous quasarsmay be suppressing star formation in their close vicinity.

DOI： 10.1093/pasj/psx112

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We construct a sample of X-ray-bright optically faint active galactic nuclei by combining Subaru Hyper Suprime-Cam, XMM-Newton, and infrared source catalogs. Fifty-three Xray sources satisfying i-band magnitude fainter than 23.5 mag and X-ray counts with the EPIC-PN detector larger than 70 are selected from 9.1 deg2, and their spectral energy distributions (SEDs) and X-ray spectra are analyzed. Forty-four objects with an X-ray to i-band flux ratio FX/Fi &gt
10 are classified as extreme X-ray-to-optical flux sources. Spectral energy distributions of 48 among 53 are represented by templates of type 2 AGNs or star-forming galaxies and show the optical signature of stellar emission from host galaxies in the source rest frame. Infrared/optical SEDs indicate a significant contribution of emission from dust to the infrared fluxes, and that the central AGN is dust obscured. The photometric redshifts determined from the SEDs are in the range of 0.6-2.5. The X-ray spectra are fitted by an absorbed power-law model, and the intrinsic absorption column densities are modest (best-fit logNH = 20.5-23.5 cm-2 in most cases). The absorptioncorrected X-ray luminosities are in the range of 6 × 1042-2 × 1045 erg s-1. Twenty objects are classified as type 2 quasars based on X-ray luminsosity and NH. The optical faintness is explained by a combination of redshifts (mostly z &gt
1.0), strong dust extinction, and in part a large ratio of dust/gas.

DOI： 10.1093/pasj/psx109

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psx046

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press  

We present the Lyα luminosity functions (LFs) at z = 5.7 and 6.6 derived from a new large sample of 1266 Lyα emitters (LAEs) identified in total areas of 14 and 21 deg2, respectively, based on the early narrowband data of the Subaru/Hyper Suprime-Cam survey. Together with careful Monte Carlo simulations that account for the incompleteness of the LAE selection and the flux estimate systematics in the narrowband imaging, we have determined the Lyα LFs with unprecedentedly small statistical and systematic uncertainties in a wide Lyα luminosity range of 1042.8-43.8 erg s-1. We obtain best-fit Schechter parameters of L∗Lyα = 1.6-0.6 +2.2 (1.7-0.7 +0.3) × 1043 erg s-1, φ∗Lyα = 0.85-0.77 +1.87 (0.47-0.44 +1.44) × 10-4 Mpc-3, and α = -2.6-0.4 +0.6 (-2.5-0.5 +0.5) at z = 5.7 (6.6). We confirm that our best-estimate Lyα LFs are consistent with the majority of the previous studies, but find that our Lyα LFs do not agree with the high number densities of LAEs recently claimed by Matthee/Santos et al.'s studies that may overcorrect the incompleteness and the flux systematics. Our Lyα LFs at z = 5.7 and 6.6 show an indication that the faint-end slope is very steep (α - -2.5), although it is also possible that the bright-end LF results are enhanced by systematic effects such as the contribution from AGNs, blended merging galaxies, and/or large ionized bubbles around bright LAEs. Comparing our Lyα LF measurements with four independent reionization models, we estimate the neutral hydrogen fraction of the intergalactic medium to be xHI = 0.3 ± 0.2 at z = 6.6, which is consistent with the small Thomson scattering optical depth obtained by Planck 2016.

DOI： 10.1093/pasj/psx131

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate the X-ray active galactic nucleus (AGN) properties of millimeter galaxies in the Great Observatories Origins Deep Survey South (GOODS-S) field detected with the Atacama Large Millimeter/submillimeter Array (ALMA), by utilizing the Chandra 7-Ms data, the deepest X-ray survey to date. Our millimeter galaxy sample comes from the ASAGAO survey covering 26 arcmin<SUP>2</SUP> (12 sources at a 1.2 mm flux-density limit of ≈ 0.6 mJy), supplemented by the deeper but narrower 1.3 mm survey of a part of the ASAGAO field by Dunlop et al. Ofthe 25 total millimeter galaxies, 14 have Chandra counterparts. The observed AGN fractions at z=1.5{--}3 are found to be {90}<SUB>-19</SUB><SUP>+8</SUP>% and {57}<SUB>-25</SUB><SUP>+23</SUP>% for the ultra-luminous and luminous infrared galaxies with log {L}<SUB>{IR</SUB>}/{L}<SUB>☉ </SUB> = 12-12.8 and log {L}<SUB>{IR</SUB>}/{L}<SUB>☉ </SUB> = 11.5-12, respectively. The majority (̃2/3) of the ALMA and/or Herschel detected X-ray AGNs at z = 1.5-3 appear to be star-formation-dominant populations, having {L}<SUB>{ { X</SUB> } }/ {L}<SUB>{IR</SUB>} ratios smaller than the “simultaneous evolution” value expected from the local black-hole-mass-to-stellar-mass ({M}<SUB>{BH</SUB>}-M <SUB>*</SUB>) relation. On the basis of the {L}<SUB>{ { X</SUB> } } and stellar mass relation, we infer that a large fraction of star-forming galaxies at z=1.5{--}3 have black hole masses that are smaller than those expected from the local {M}<SUB>{BH</SUB>}-M <SUB>*</SUB> relation. This contrasts previous reports on luminous AGNs at the same redshifts detected in wider and shallower surveys, which are subject to selection biases against lower luminosity AGNs. Our results are consistent with an evolutionary scenario in which star formation occurs first, and an AGN-dominant phase follows later, in objects that finally evolve into galaxies with classical bulges....

DOI： 10.3847/1538-4357/aa9f10

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

We present the ionized gas properties of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme optical/IR color, (i - [22])AB &gt
7.0, selected with the Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE). For 36 IR-bright DOGs that show [O iii]λ5007 emission in the SDSS spectra, we performed a detailed spectral analysis to investigate their ionized gas properties. In particular, we measured the velocity offset (the velocity with respect to the systemic velocity measured from the stellar absorption lines) and the velocity dispersion of the [O iii] line. We found that the derived velocity offset and dispersion of most IR-bright DOGs are larger than those of Seyfert 2 galaxies (Sy2s) at z &lt
0.3, meaning that the IR-bright DOGs show relatively strong outflows compared to Sy2s. This can be explained by the difference in IR luminosity contributed from active galactic nuclei, (AGN), because we found that (i) (AGN) correlates with the velocity offset and dispersion of [O iii] and (ii) our IR-bright DOG sample has larger (AGN) than Sy2s. Nevertheless, the fact that about 75% IR-bright DOGs have a large (&gt
300 km s-1) velocity dispersion, which is a larger fraction compared to other AGN populations, suggests that IR-bright DOGs are good laboratories to investigate AGN feedback. The velocity offset and dispersion of [O iii] and [Ne iii]λ3869 are larger than those of [O ii]λ3727, which indicates that the highly ionized gas tends to show stronger outflows.

DOI： 10.3847/1538-4357/aa918a

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We present rest-frame optical spectra of 12 "nitrogen-loud" quasars at z similar to 2.2, whose rest-frame ultraviolet (UV) spectra show strong nitrogen broad emission lines. To investigate their narrow-line region (NLR) metallicities, we measure the equivalent width (EW) of the [O III]lambda 5007 emission line: if the NLR metallicity is remarkably high, as suggested by the strong UV nitrogen lines, the [O III]lambda 5007 line flux should be very weak due to the low equilibrium temperature of the ionized gas owing to significant metal cooling. In the result we found that our spectra show moderate EW of the [O III]lambda 5007 line similar to general quasars. This indicates that nitrogen-loud quasars do not have extremely metal-rich gas clouds in NLRs. This suggests that strong nitrogen lines from broad-line regions (BLRs) originate from exceptionally high abundances of nitrogen relative to oxygen without very high BLR metallicities. This result indicates that broad emission lines of nitrogen are not good indicators of the BLR metallicity in some cases. On the other hand, we also investigate virial black hole masses and Eddington ratios by using the H beta and C IV lambda 1549 lines for our sample. As a result, we found that black hole masses and Eddington ratios of nitrogen-loud quasars tend to be low and high relative to normal quasars, suggesting that nitrogen-loud quasars seem to be in a rapidly accreting phase. This can be explained in terms of a positive correlation between Eddington ratios and nitrogen abundances of quasars, which is probably caused by the connection between the mass accretion onto black holes and nuclear star formation.

DOI： 10.1051/0004-6361/201629878

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We report the discovery of an infrared (IR)-bright dust-obscured galaxy (DOG) that shows a strong ionized-gas outflow but no significant molecular gas outflow. Based on detailed analysis of their optical spectra, we found some peculiar IR-bright DOGs that show strong ionized-gas outflow ([O III] lambda 5007) from the central active galactic nucleus (AGN). For one of these DOGs (WISE J102905.90+050132.4) at z(spec) = 0.493, we performed follow-up observations using ALMA to investigate their CO molecular gas properties. As a result, we successfully detected (CO)-C-12(J = 2-1) and (CO)-C-12(J = 4-3) lines and the continuum of this DOG. The intensity-weighted velocity map of both lines shows a gradient, and the line profile of those CO lines is well-fitted by a single narrow Gaussian, meaning that this DOG has no sign of strong molecular gas outflow. The IR luminosity of this object is log (L-IR/L-circle dot) = 12.40, which is classified as an ultraluminous IR galaxy (ULIRG). We found that (i) the stellar mass and star formation rate relation and (ii) the CO luminosity and far-IR luminosity relation are consistent with those of typical ULIRGs at similar redshifts. These results indicate that the molecular gas properties of this DOG are normal despite the fact that its optical spectrum shows a powerful AGN outflow. We conclude that a powerful ionized-gas outflow caused by the AGN does not necessarily affect the cold interstellar medium in the host galaxy, at least for this DOG.

DOI： 10.3847/1538-4357/aa9d17

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We study the heating mechanisms and Lyα escape fractions of 35 Lyα blobs (LABs) at z ≈ 3.1 in the SSA22 field. Dust continuum sources have been identified in 11 of the 35 LABs, all with star formation rates (SFRs) above 100 M <SUB>☉</SUB> yr<SUP>-1</SUP>. Likely radio counterparts are detected in 9 out of 29 investigated LABs. The detection of submillimeter dust emission is more linked to the physical size of the Lyα emission than to the Lyα luminosities of the LABs. A radio excess in the submillimeter/radio-detected LABs is common, hinting at the presence of active galactic nuclei. Most radio sources without X-ray counterparts are located at the centers of the LABs. However, all X-ray counterparts avoid the central regions. This may be explained by absorption due to exceptionally large column densities along the line-of-sight or by LAB morphologies, which are highly orientation dependent. The median Lyα escape fraction is about 3% among the submillimeter-detected LABs, which is lower than a lower limit of 11% for the submillimeter-undetected LABs. We suspect that the large difference is due to the high dust attenuation supported by the large SFRs, the dense large-scale environment as well as large uncertainties in the extinction corrections required to apply when interpreting optical data....

DOI： 10.3847/1538-4357/aa960f

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1017/pasa.2017.48

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CAMBRIDGE UNIV PRESS  

The physical processes driving the chemical evolution of galaxies in the last similar to 11Gyr cannot be understood without directly probing the dust-obscured phase of star-forming galaxies and active galactic nuclei. This phase, hidden to optical tracers, represents the bulk of the star formation and black hole accretion activity in galaxies at 1 &lt; z &lt; 3. Spectroscopic observations with a cryogenic infrared observatory like SPICA, will be sensitive enough to peer through the dust-obscured regions of galaxies and access the rest-frame mid- to far-infrared range in galaxies at high-z. This wavelength range contains a unique suite of spectral lines and dust features that serve as proxies for the abundances of heavy elements and the dust composition, providing tracers with a feeble response to both extinction and temperature. In this work, we investigate how SPICA observations could be exploited to understand key aspects in the chemical evolution of galaxies: the assembly of nearby galaxies based on the spatial distribution of heavy element abundances, the global content of metals in galaxies reaching the knee of the luminosity function up to z similar to 3, and the dust composition of galaxies at high-z. Possible synergies with facilities available in the late 2020s are also discussed.

DOI： 10.1017/pasa.2017.43

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We constrain the quasar contribution to the cosmic reionization based on our deep optical survey of z similar to 6 quasars down to z(R) = 24.15 using Subaru/Suprime-Cam in three UKIDSS-DXS fields covering 6.5 deg(2). In Kashikawa et al. (2015), we select 17 quasar candidates and report our initial discovery of two low-luminosity quasars (M-1450 similar to -23) from seven targets, one of which might be a Ly alpha-emitting galaxy. From an additional optical spectroscopy, none of the four candidates out of the remaining 10 turn out to be genuine quasars. Moreover, the deeper optical photometry provided by the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) shows that, unlike the two already-known quasars, the i - z and z - y colors of the last six candidates are consistent with M-or L-type brown dwarfs. Therefore, the quasar luminosity function (QLF) measurement in the previous paper is confirmed. Compiling the QLF measurements from the literature over a wide magnitude range, including an extremely faint AGN candidate from Parsa et al. (2017), to fit them with a double power law, we find that the bestfit faint-end slope is alpha = -2.04(-0.18)(+0.33) (-1.98(-0.18)(+0.48)) and characteristic magnitude is M-1450* = -25.8(-1.9)(+1.1) (-25.7(-1.8)(+1.0)) in the case of two (one) quasar detection. Our result suggests that, if the QLF is integrated down to M1450 = -18, quasars produce similar to 1%-12% of the ionizing photons required to fully ionize the universe at z similar to 6 with a 2 sigma confidence level, assuming that the escape fraction is f(esc) = 1 and the intergalactic medium clumpy factor is C = 3. Even when the systematic uncertainties are taken into account, our result supports the scenario that quasars are the minor contributors of the reionization.

DOI： 10.3847/2041-8213/aa8cc6

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present near-IR spectroscopy of 22 luminous low-ionization broad absorption line quasars (LoBAL QSOs) at redshift 1.3 &lt; z &lt; 2.5, with 12 objects at z similar to 1.5 and 10 at z similar to 2.3. The spectra cover the rest-frame H alpha and H beta line regions, allowing us to obtain robust black hole mass estimates based on the broad H alpha line. We use these data, augmented by a lower-redshift sample from the Sloan Digital Sky Survey, to test the proposed youth scenario for LoBALs, which suggests that LoBALs constitute an early short-lived evolutionary stage of quasar activity, by probing for any difference in their masses, Eddington ratios, or rest-frame optical spectroscopic properties compared to normal quasars. In addition, we construct the UV to mid-IR spectral energy distributions (SEDs) for the LoBAL sample and a matched non-BAL quasar sample. We do not find any statistically significant difference between LoBAL QSOs and non-BAL QSOs in their black hole mass or Eddington ratio distributions. The mean UV to mid-IR SED of the LoBAL QSOs is consistent with non-BAL QSOs, apart from their stronger reddening. At z &gt; 1 there is no clear difference in their optical emission line properties. We do not see particularly weak [O III] or strong Fe II emission. The LoBAL QSOs do not show a stronger prevalence of ionized gas outflows as traced by the [O III] line, compared to normal QSOs of similar luminosity. We conclude that the optical-MIR properties of LoBAL QSOs are consistent with the general quasar population and do not support them to constitute a special phase of active galactic nucleus evolution.

DOI： 10.3847/1538-4357/aa8e4c

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present the result of our spectroscopic follow-up observation for faint quasar candidates at z similar to 5 in part of the Canada-France-Hawaii Telescope Legacy Survey wide field. We select nine photometric candidates and identify three z similar to 5 faint quasars, one z similar to 4 faint quasar, and a late-type star. Since two faint quasar spectra show the C. IV emission line without suffering from a heavy atmospheric absorption, we estimate their black hole masses (M-BH) and Eddington ratios (L/L-Edd). The inferred log M-BH are 9.04 +/- 0.14 and 8.53 +/- 0.20, respectively. In addition, the inferred log(L/L-Edd) are - 1.00 +/- 0.15 and -0.42 +/- 0.22, respectively. If we adopt that L/L-Edd constant or proportional to(1 + z)(2), the seed black hole masses (M-seed) of our z similar to 5 faint quasars are expected to be &gt; 10(5) M-circle dot in most cases. We also compare the observational results with a mass accretion model, where angular momentum is lost due to supernova explosions. Accordingly, M-BH of the z similar to 5 faint quasars in our sample can be explained even if M-seed is similar to 10(3) M-circle dot. Since z similar to 6 luminous qusars and our z similar to 5 faint quasars are not on the same evolutionary track, z similar to 6 luminous quasars and our z similar to 5 quasars are not the same populations but different populations, due to the difference of a period of the mass supply from host galaxies. Furthermore, we confirm that one can explain M-BH of z similar to 6 luminous quasars and our z similar to 5 faint quasars even if their seed black holes are formed at z similar to 7.

DOI： 10.3847/1538-4357/aa83ae

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We study the properties of dark matter halos that contain star-forming galaxies at 1.43 &lt;= z &lt;= 1.74, using the FMOS-COSMOS survey. The sample consists of 516 objects with a detection of the Ha emission line, which represent the star forming population at this epoch, having a stellar mass range of 10(9.57) &lt;= M*/M circle dot less than or similar to 10(11.4) and a star-formation rate range of 15 less than or similar to SFR/(Me-circle dot yr(-1)) less than or similar to 600. We measure the projected two-point correlation function while carefully taking into account observational biases, and find a significant clustering amplitude at scales of 0.04-10 h(-1) cMpc, with a correlation length r(0) = 5.26(-0.62)(+0.75) h(-1) cMpc and a bias b = 2.44(-0.32)(+0.38) We interpret our clustering measurement using a halo occupation distribution model. The sample galaxies appear to reside in halos with mass M-h = 4.71 (+1.19)(-1.62) x 10(12) h(-1) M-circle dot on average, which will likely become present-day halos of mass M-h (z =0) similar to 2 x 10(13) h(-1) M-circle dot, equivalent to the typical halo mass scale of galaxy groups. We then confirm the decline of the stellar-to-halo mass ratio at M-h &lt; 10(12) M-circle dot, finding M-*/M-h approximate to 5 x 10(-3) at M-h = 7.5 x 10(11) M-circle dot, which is lower by a factor of 2-4 than those measured at higher masses (M-h similar to 10(12-13) Me-circle dot). Finally, we use our results to illustrate the future capabilities of Subaru's Prime-Focus Spectrograph, a next-generation instrument that will provide strong constraints on the galaxy-formation scenario by obtaining precise measurements of galaxy clustering at z &gt; 1.

DOI： 10.3847/1538-4357/aa789d

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

We report the ALMA observations of the most massive (star-forming) galaxy in the redshift range 3 &lt; z &lt; 4 within the whole Great Observatories Origins Deep Survey South field (GOODS-S) field. We detect a large elongated structure of molecular gas around the massive primeval galaxy, traced by the CO(4-3) emission, and extended over 40 kpc. We infer a mass of the large gaseous structure of M-gas similar to 2-6 x 10(11) M-circle dot. About 60 per cent of this mass is not directly associated with either the central galaxy or its two lower mass satellites. The CO extended structure is also detected in continuum thermal emission. The kinematics of the molecular gas shows the presence of different components, which cannot be ascribed to simple rotation. Furthermore, on even larger scales, we detect nine additional CO systems within a radius of 250 kpc from the massive galaxy and mostly distributed in the same direction as the CO elongated structure found in the central 40 kpc. The stacked images of these CO systems show detections in the thermal continuum and in the X-rays, suggesting that these systems are forming stars at a rate of 30-120 M-circle dot yr(-1). We suggest that the extended gas structure, combined with its kinematic properties, and the gas-rich star-forming systems detected on larger scales, are tracing the inner and densest regions of large-scale accreting streams, feeding the central massive galaxy. These results corroborate models of galaxy formation, in which accreting streams are clumpy and undergo some star formation (hence enriching the streams with metals) even before accreting onto the central galaxy.

DOI： 10.1093/mnras/stx712

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

In order to investigate the physical relationship between strong Ly alpha absorbers (log N-HI &gt;= 20.0 cm(-2)) such as damped Ly a absorption systems (DLAs) and young star-forming galaxies at high redshift, we have conducted narrow-band observations of Ly a emitters (LAEs) in a concentrated region of strong Ly alpha absorbers at z = 2.3, the J1230+34 field. Using a catalog of Ly alpha absorbers with log N-HI &gt;= 20.0 cm(-2) based on the Baryon Oscillation Spectroscopic Survey, we found six fields where three or more absorbers are concentrated within a (50 Mpc)(3) cubic box in the comoving scale. Among them, we focus on the J1230+34 field, where two DLAs and two sub-DLAs are present. Our narrow-band imaging observations with Subaru/Suprime-Cam using a custom-made filter, NB400 (lambda(c) = 4003 angstrom and FWHM = 92 angstrom) yield a sample of 149 LAEs in this field. In the large scale (similar to 50 Mpc), we have found no differences between the obtained Ly a luminosity function and those in the blank fields at similar redshifts. We also compare the frequency distribution of the Ly a rest-frame equivalent width (EW0) in the target field and other fields including both overdensity region and blank field, but find no differences. On the other hand, in the small scale (similar to 10 Mpc), we have found a possible overdensity of LAEs around a DLA with the highest HI column density (N-HI = 21.08 cm(-2)) in the target field while there are no density excesses around the other absorbers with a lower N-HI.

DOI： 10.1093/pasj/psx027

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report the identification of four millimeter line-emitting galaxies with the Atacama Large Milli/submillimeter Array (ALMA) in SSA22 Field (ADF22). We analyze the ALMA 1.1-mm survey data, with an effective survey area of 5 arcmin<SUP>2</SUP>, frequency ranges of 253.1-256.8 and 269.1-272.8 GHz, angular resolution of 0{^''<SUB>.</SUB>}7 and rms noise of 0.8 mJy beam<SUP>-1</SUP> at 36 km s<SUP>-1</SUP> velocity resolution. We detect four line-emitter candidates with significance levels above 6σ. We identify one of the four sources as a CO(9-8) emitter at z = 3.1 in a member of the proto-cluster known in this field. Another line emitter with an optical counterpart is likely a CO(4-3) emitter at z = 0.7. The other two sources without any millimeter continuum or optical/near-infrared counterpart are likely to be [C II] emitter candidates at z = 6.0 and 6.5. The equivalent widths of the [C II] candidates are consistent with those of confirmed high-redshift [C II] emitters and candidates, and are a factor of 10 times larger than that of the CO(9-8) emitter detected in this search. The [C II] luminosity of the candidates are 4-7 × 10<SUP>8</SUP> L<SUB>☉</SUB>. The star formation rates (SFRs) of these sources are estimated to be 10-20 M<SUB>☉</SUB> yr<SUP>-1</SUP> if we adopt an empirical [C II] luminosity-SFR relation. One of them has a relatively low S/N ratio, but shows features characteristic of emission lines. Assuming that at least one of the two candidates is a [C II] emitter, we derive a lower limit of [C II]-based star formation rate density (SFRD) at z ̃ 6. The resulting value of &gt;10<SUP>-2</SUP> M<SUB>☉</SUB> yr<SUP>-1</SUP> Mpc<SUP>-3</SUP> is consistent with the dust-uncorrected UV-based SFRD. Future millimeter/submillimeter surveys can be used to detect a number of high-redshift line emitters, with which to study the star formation history in the early universe....

DOI： 10.1093/pasj/psx018

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Low-metallicity active galactic nuclei (AGNs) are interesting to study for the early phase of AGN evolution. However, most AGNs are chemically matured, and accordingly, low-metallicity AGNs are extremely rare. One approach to search for low-metallicity AGNs systematically is utilizing the so-called BPT diagram that consists of the [O III]lambda 5007/H alpha lambda 4861 and [N II] lambda 6584/H alpha lambda 6563 flux ratios. Specifically, photoionization models predict that low-metallicity AGNs show a high [O III]lambda 5007/H beta lambda 4861 ratio and a relatively low [N II]lambda 6584/H alpha lambda 6563 ratio that corresponds to the location between the sequence of star-forming galaxies and that of usual AGNs on the BPT diagram (hereafter "the BPT valley"). However, other populations of galaxies such as star-forming galaxies and AGNs with a high electron density or a high-ionization parameter could be also located in the BPT valley, not only low-metallicity AGNs. In this paper, we examine whether most of the emission-line galaxies at the BPT valley are low-metallicity AGNs or not. We select 70 BPT-valley objects from 212,866 emission-line galaxies obtained by the Sloan Digital Sky Survey. Among the 70 BPT-valley objects, 43 objects show firm evidence of the AGN activity, i.e., the He II lambda 4686 emission and/or weak but significant broad Ha emission. Our analysis shows that those 43 BPT-valley AGNs are not characterized by a very high gas density nor ionization parameter, inferring that at least 43 among 70 BPT-valley objects (i.e., &gt; 60%) are low-metallicity AGNs. This suggests that the BPT diagram is an efficient tool to search for low-metallicity AGNs.

DOI： 10.3847/1538-4357/aa70e1

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We investigate the star-forming activity of a sample of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme red color in the optical and IR regime, (i - [22])(AB) &gt; 7.0. Combining an IR-bright DOG sample with the flux at 22 mu m. &gt; 3.8 mJy discovered by Toba & Nagao with the IRAS faint source catalog version 2 and AKARI far-IR (FIR) all-sky survey bright source catalog version 2, we selected 109 DOGs with FIR data. For a subsample of seven IR-bright DOGs with spectroscopic redshifts (0.07 &lt; z &lt; 1.0) that were obtained from the literature, we estimated their IR luminosity, star formation rate (SFR), and stellar mass based on the spectral energy distribution fitting. We found that (1) the WISE 22 mu m luminosity at the observed frame is a good indicator of IR luminosity for IR-bright DOGs and (2) the contribution of the active galactic nucleus to IR luminosity increases with IR luminosity. By comparing the stellar mass and SFR relation for our DOG sample and the literature, we found that most of the IR-bright DOGs lie significantly above the main sequence of star-forming galaxies at similar redshift, indicating that the majority of IRAS-or AKARI-detected IR-bright DOGs are starburst galaxies.

DOI： 10.3847/1538-4357/aa6d0a

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出版者・発行元：The Korean Astronomical Society  

DOI： 10.5303/pkas.2017.32.1.317

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

We report the serendipitous discovery of a quadruply lensed source at z(s) = 3.76, HSC J115252+004733, from the Hyper Suprime-Cam (HSC) Survey. The source is lensed by an early-type galaxy at z(1) = 0.466 and a satellite galaxy. Here, we investigate the properties of the source by studying its size and luminosity from the imaging and the luminosity and velocity width of the Ly-alpha line from the spectrum. Our analyses suggest that the source is most probably a low-luminosity active galactic nucleus (LLAGN) but the possibility of it being a compact bright galaxy (e.g. a Lyman-alpha emitter or lyman break galaxy) cannot be excluded. The brighter pair of lensed images appears point-like except in the HSC i band (with a seeing similar to 0.5 arcsec). The extended emission in the i-band image could be due to the host galaxy underneath the AGN, or alternatively, due to a highly compact lensed galaxy (without AGN) which appears point-like in all bands except in i band. We also find that the flux ratio of the brighter pair of images is different in the Ks band compared to optical wavelengths. Phenomena such as differential extinction and intrinsic variability cannot explain this chromatic variation. While microlensing from stars in the foreground galaxy is less likely to be the cause, it cannot be ruled out completely. If the galaxy hosts an AGN, then this represents the highest redshift quadruply imaged AGN known to date, enabling study of a distant LLAGN. Discovery of this unusually compact and faint source demonstrates the potential of the HSC survey.

DOI： 10.1093/mnras/stw2924

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present measurements of the clustering properties of a sample of infrared (IR) bright dust-obscured galaxies (DOGs). Combining 125 deg(2) of wide and deep optical images obtained with the Hyper Suprime-Cam on the Subaru Telescope and all-sky mid-IR images taken with Wide-Field Infrared Survey Explorer, we have discovered 4367 IR-bright DOGs with (i - [22])(AB) &gt; 7.0 and flux density at 22 mu m &gt; 1.0 mJy. We calculate the angular autocorrelation function (ACF) for a uniform subsample of 1411 DOGs with 3.0 mJy &lt; flux (22 mu m) &lt; 5.0 mJy and i(AB) &lt; 24.0. The ACF of our DOG subsample is well-fit with a single power law, w(theta) = (0.010 +/- 0.003)theta(-0.9), where theta is in degrees. The correlation amplitude of IR-bright DOGs is larger than that of IR-faint DOGs, which reflects a flux dependence of the DOG clustering, as suggested by Brodwin et al. We assume that the redshift distribution for our DOG sample is Gaussian, and consider two cases: (1) the redshift distribution is the same as IR-faint DOGs with flux at 22 mu m &lt; 1.0 mJy, mean and sigma z = 1.99 +/- 0.45, and (2) z = 1.19 +/- 0.30, as inferred from their photometric redshifts. The inferred correlation length of IR-bright DOGs is r(0) = 12.0 +/- 2.0 and 10.3 +/- 1.7 h(-1) Mpc, respectively. IR-bright DOGs reside in massive dark matter halos with a mass of log [ M-h /(h(-1) M-circle dot)] = 13.57(-0.55)(+0.50) and 13.65(-0.52)(+0.45) in the two cases, respectively.

DOI： 10.3847/1538-4357/835/1/36

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Outflows in active galactic nuclei (AGNs) are crucial to understand in investigating the co-evolution of supermassive black holes (SMBHs) and their host galaxies since outflows may play an important role as an AGN feedback mechanism. Based on archival UV spectra obtained with the Hubble Space Telescope and IUE, we investigate outflows in the broad-line region (BLR) in low-redshift AGNs (z &lt; 0.4) through detailed analysis of the velocity profile of the C IV emission line. We find a dependence of the outflow strength on the Eddington ratio and the BLR metallicity in our low-redshift AGN sample, which is consistent with earlier results obtained for high-redshift quasars. These results suggest that BLR outflows, gas accretion onto SMBHs, and past star formation activity in host galaxies are physically related in low-redshift AGNs as in powerful high-redshift quasars.

DOI： 10.3847/1538-4357/835/1/24

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/2041-8213/834/2/L16

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

One of the important unsettled problems regarding active galactic nuclei (AGNs) is the major ionization mechanism of gas clouds in AGN narrow-line regions (NLRs). In order to investigate this issue, we present our J-band spectroscopic observations of a sample of 26 nearby Seyfert galaxies. In our study, we use the flux ratio of the following two forbidden emission lines, [Fe ii]1.257 μm and [P ii]1.188 μm, because it is known that this ratio is sensitive to the ionization mechanism. We obtain the [Fe ii]/[P ii] flux ratio or its lower limit for 19 objects. In addition to our data, we compile this flux ratio (or its lower limit) for 23 nearby Seyfert galaxies from the literature. Based on the collected data, we find that three Seyfert galaxies show very large lower limits of the [Fe ii]/[P ii] flux ratios (≳10): NGC 2782, NGC 5005, and Mrk 463. It is thus suggested that the contribution of the fast shock in the gas excitation is significantly large for them. However, more than half of the Seyfert galaxies in our sample show moderate [Fe ii]/[P ii] flux ratios (∼2), which is consistent with pure photoionization by power-law ionizing continuum emission. We also find that the [Fe ii]/[P ii] flux ratio shows no clear correlation with the radio loudness, suggesting that the radio jet is not the primary origin of shocks in NLRs of Seyfert galaxies.

DOI： 10.3847/1538-4357/833/2/190

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Recent studies have derived quasar luminosity functions (QLFs) at various redshifts. However, the faint side of the QLF at high redshifts is still too uncertain. An accurate estimate of the survey completeness is essential to derive an accurate QLF for use in studying the luminosity-dependent density evolution (LDDE) of the quasar population. Here we investigate how the luminosity dependence of quasar spectra (the Baldwin effect) and the attenuation model for the intergalactic medium (IGM) affect the completeness estimates. For this purpose, we specifically revisit the completeness of quasar surveys at z similar to 4-5, using the COSMOS images observed with Subaru/Suprime-Cam. As a result, we find that the completeness estimates are sensitive to the luminosity dependence of the quasar spectrum and to different the IGM attenuation models. At z similar to 4, the number density of quasars when we adopt the latest IGM model and take the luminosity dependence of spectra into account is (3.49 +/- 1.62) x 10(-7) Mpc(-3) mag(-1) for -24.09 &lt; M-1450 &lt; -23.09 and (5.24 +/- 2.13) x 10(-7) Mpc(-3) mag(-1) for -23.09 &lt; M-1450 &lt; -22.09, which are similar to 24% lower than that estimated by the conventional method. On the other hand, at z similar to 5, the 1 sigma confidence upper limit of the number density at -24.5 &lt; M-1450 &lt; -22.5 in our new estimates is similar to 43% higher than that estimated previously. The results suggest that the luminosity dependence of the quasar spectrum and the IGM model are important for deriving the accurate number density of high-z quasars. Even taking these effects into account, the inferred LDDE of quasars is consistent with the AGN downsizing evolutionary picture.

DOI： 10.3847/0004-637X/832/2/208

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present the first results from MMT and Keck spectroscopy for a large sample of 0.1 &lt;= z &lt;= 1 emission-line galaxies selected from our narrowband imaging in the Subaru Deep Field. We measured the weak [O III] lambda 4363 emission line for 164 galaxies (66 with at least 3 sigma detections, and 98 with significant upper limits). The strength of this line is set by the electron temperature for the ionized gas. Because the gas temperature is regulated by the metal content, the gas-phase oxygen abundance is inversely correlated with [O III] lambda 4363 line strength. Our temperature-based metallicity study is the first to span approximate to 8 Gyr of cosmic time and approximate to 3 dex in stellar mass for low-mass galaxies, log(M-star/M-circle dot) approximate to 6.0-9.0. Using extensive multi-wavelength photometry, we measure the evolution of the stellar mass-gas metallicity relation and its dependence on dust-corrected star formation rate ( SFR). The latter is obtained from high signal-to-noise Balmer emission-line measurements. Our mass-metallicity relation is consistent with Andrews & Martini at z &lt;= 0.3, and evolves toward lower abundances at a given stellar mas log (O/H) alpha(1+z)(-2.32-0.26+0.52) We find that galaxies with lower metallicities have higher SFRs at a given stellar mass and redshift, although the scatter is large (approximate to 0.3 dex) and the trend is weaker than seen in local studies. We also compare our mass-metallicity relation against predictions from high-resolution galaxy formation simulations, and find good agreement with models that adopt energy- and momentum-driven stellar feedback. We identified 16 extremely metal-poor galaxies with abundances of less than a tenth of solar; our most metal-poor galaxy at z approximate to 0.84 is similar to I Zw 18.

DOI： 10.3847/0004-637X/828/2/67

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/0004-637X/828/1/26

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

Negative feedback from active galactic nuclei (AGN) is considered a key mechanism in shaping galaxy evolution. Fast, extended outflows are frequently detected in the AGN host galaxies at all redshifts and luminosities, both in ionised and molecular gas. However, these outflows are only potentially able to quench star formation, and we are still lacking decisive evidence of negative feedback in action. Here we present observations obtained with the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) H- and K-band integral-field of two quasars at z similar to 2.4 that are characterised by fast, extended outflows detected through the [OIII]lambda 5007 line. The high signal-to-noise ratio of our observations allows us to identify faint narrow (FWHM &lt; 500 km s(-1)) and spatially extended components in [OIII]lambda 5007 and H alpha emission associated with star formation in the host galaxy. This star formation powered emission is spatially anti-correlated with the fast outflows. The ionised outflows therefore appear to be able to suppress star formation in the region where the outflow is expanding. However, the detection of narrow spatially extended H alpha emission indicates star formation rates of at least similar to 50-90 M-circle dot yr(-1), suggesting either that AGN feedback does not affect the whole galaxy or that many feedback episodes are required before star formation is completely quenched. On the other hand, the narrow H alpha emission extending along the edges of the outflow cone may also lead also to a positive feedback interpretation. Our results highlight the possible double role of galaxy-wide outflows in host galaxy evolution.

DOI： 10.1051/0004-6361/201528037

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

We present a new method for effectively selecting objects which may be low-mass active black holes (BHs) at galaxy centers using high-cadence optical imaging data, and our first spectroscopic identification of an active 2.7 x 10(6) M-circle dot BH at z = 0.164. This active BH was originally selected due to its rapid optical variability, from a few hours to a day, based on Subaru Hyper Suprime-Cam g-band imaging data taken with a 1 hr cadence. Broad and narrow Ha lines and many other emission ones are detected in our optical spectra taken with Subaru FOCAS, and the BH mass is measured via the broad Ha emission line width (1880 kms(-1)) and luminosity (4.2 x 1040 erg s(-1)) after careful correction to the atmospheric absorption around 7580-7720 angstrom. We measure the Eddington ratio and find it to be as low as 0.05, considerably smaller than those in a previous SDSS sample with similar BH mass and redshift, which indicates one of the special potentials of our Subaru survey. The g - r color and morphology of the extended component indicate that the host galaxy is a star-forming galaxy. We also show the effectiveness of our variability selection for low-mass active BHs.

DOI： 10.1093/pasj/psw033

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present rapidly rising transients discovered by a high-cadence transient survey with the Subaru telescope and Hyper Suprime-Cam. We discovered five transients at z = 0.384-0.821, showing a rate of rise faster than 1 mag per day in the restframe near-ultraviolet wavelengths. The fast rate of rise and brightness are most similar to SN 2010aq and PS1-13arp, for which ultraviolet emission was detected within a few days after the shock breakout. The lower limit of the event rate of rapidly rising transients is similar to 9% of core-collapse supernova rates, assuming the duration of rapid rise to be 1 day. We show that the light curves of the three faint objects agree with the cooling envelope emission from the explosion of red supergiants. The other two luminous objects, however, are brighter and faster than the cooling envelope emission. We interpret these two objects to be the shock breakout from a dense wind with a mass loss rate of similar to 10(-3) M-circle dot yr(-1), as also proposed for PS1-13arp. This mass loss rate is higher than that typically observed for red supergiants. The event rate of these luminous objects is greater than or similar to 1% of the core-collapse supernova rate, and thus our study implies that more than similar to 1% of massive stars can experience intense mass loss a few years before the explosion.

DOI： 10.3847/0004-637X/819/1/5

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We aim to search for hyperluminous infrared (IR) galaxies (HyLIRGs) with IR luminosity L-IR &gt; 10(13) L-circle dot by applying the selection method of dust-obscured galaxies (DOGs). They are spatially rare but could correspond to a maximum phase of cosmic star formation (SF) and/or active galactic nucleus (AGN) activity;. hence, they are a crucial population for understanding the SF and mass assembly history of galaxies. Combining the optical and IR catalogs obtained from the. Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE), we performed the extensive HyLIRGs survey; we selected 5311 IR-bright DOGs with i - [22] &gt; 7.0 and flux at 22 mu m &gt; 3.8 mJy in 14,555 deg(2), where i and [22] are i-band and 22 mu m AB magnitudes, respectively. Among them, 67 DOGs have reliable spectroscopic redshifts that enable us to estimate their total IR luminosity based on the spectral energy distribution fitting. Consequently, we successfully discovered 24 HyLIRGs among the 67 spectroscopically confirmed DOGs. We found that (i) i - [22] color of IR-bright DOGs correlates with the total IR luminosity and (ii) the. surface number density of HyLIRGs is &gt; 0.17 deg-2. A large. fraction (similar to 73%) of IR-bright DOGs with i - [22] &gt; 7.5 show. L-IR &gt; 10(13) L-circle dot, and the DOG. criterion we adopted could be independently effective against the. "W1W2-dropout method," based on four WISE bands, for searching hyperluminous IR populations of galaxies.

DOI： 10.3847/0004-637X/820/1/46

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We investigate morphological properties of 61 Ly alpha emitters (LAEs) at z = 4.86 identified in the COSMOS field, based on Hubble Space Telescope Advanced Camera for Surveys (ACS) imaging data in the F814W band. Out of the 61 LAEs, we find the ACS counterparts for 54 LAEs. Eight LAEs show double-component structures with a mean projected separation of 0 ''.163 (similar to 4.0 kpc at z = 4.86). Considering the faintness of these ACS sources, we carefully evaluate their morphological properties, that is, size and ellipticity. While some of them are compact and indistinguishable from the point-spread function (PSF) half-light radius of 0 ''.107 (similar to 0.45 kpc), the others are clearly larger than the PSF size and spatially extended up to 0 ''.13 (similar to 1.9 kpc). We find that the ACS sources show a positive correlation between ellipticity and size and that the ACS sources with large size and round shape are absent. Our Monte Carlo simulation suggests that the correlation can be explained by (1) the deformation effects via PSF broadening and shot noise or (2) the source blending in which two or more sources with small separation are blended in our ACS image and detected as a single elongated source. Therefore, the 46 single-component LAEs could contain the sources that consist of double (or multiple) components with small spatial separation (i.e., &lt;0 ''.3 or 1.9 kpc). Further observation with high angular resolution at longer wavelengths (e.g., rest-frame wavelengths of greater than or similar to 4000 angstrom) is inevitable to decipher which interpretation is adequate for our LAE sample.

DOI： 10.3847/0004-637X/819/1/25

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

We present the results of new infrared spectroscopic observations of 37 quasars at z similar to 3, selected based on the optical r '-bandmagnitude and the availability of nearby bright stars for future imaging follow-up with an adaptive optics system. The supermassive black hole (SMBH) masses (M-BH) were successfully estimated in 28 out of 37 observed objects from the combination of the H beta emission linewidth and continuum luminosity at rest-frame 5100 angstrom. Comparing these results with those from previous studies of quasars with similar redshift, our sample exhibited slightly lower Eddington ratios (similar to-0.11 dex in median), and the SMBH masses are slightly higher (similar to 0.38 dex in median). The SMBH growth time, tgrow, was calculated by dividing the estimated SMBH mass by the mass accretion rate measured using optical luminosity. We found, given reasonable assumptions, that t(grow) was smaller than the age of the universe at the redshift of individual quasars for a large fraction of observed sources, suggesting that the SMBHs in many of our observed quasars are in the growing phase with high accretion rates. A comparison of the SMBH masses derived from our H beta data and archived CIV data indicated considerable scattering, as indicated in previous studies. All quasars with measured SMBH masses have at least one nearby bright star, such that they are suitable targets for adaptive optics observations to study the mass relationship between SMBHs and host galaxies' stellar components at high redshift.

DOI： 10.1093/pasj/psv102

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

Aims. The aim of this paper is to test the basic model of negative active galactic nuclei (AGN) feedback. According to this model, once the central black hole accretes at the Eddington limit and reaches a certain critical mass, AGN driven outflows blow out gas, suppressing star formation in the host galaxy and self-regulating black hole growth.
Methods. We consider a sample of 224 quasars selected from the Sloan Digital Sky Survey (SDSS) at z &lt; 1 observed in the infrared band by the Herschel Space Observatory in point source photometry mode. We evaluate the star formation rate in relation to several outflow signatures traced by the [O III] lambda 4959, 5007 and [O II] lambda 3726, 3729 emission lines in about half of the sample with high quality spectra.
Results. Most of the quasars show asymmetric and broad wings in [O III], which we interpret as outflow signatures. We separate the quasars in two groups, "weakly" and "strongly" outflowing, using three different criteria. When we compare the mean star formation rate in five redshift bins in the two groups, we find that the star formation rate (SFR) are comparable or slightly larger in the strongly outflowing quasars. We estimate the stellar mass from spectral energy distribution (SED) fitting and the quasars are distributed along the star formation main sequence, although with a large scatter. The scatter from this relation is uncorrelated with respect to the kinematic properties of the outflow. Moreover, for quasars dominated in the infrared by starburst or by AGN emission, we do not find any correlation between the star formation rate and the velocity of the outflow, a trend previously reported in the literature for pure starburst galaxies.
Conclusions. We conclude that the basic AGN negative feedback scenario seems not to agree with our results. Although we use a large sample of quasars, we did not find any evidence that the star formation rate is suppressed in the presence of AGN driven outflows on large scale. A possibility is that feedback is effective over much longer timescales than those of single episodes of quasar activity.

DOI： 10.1051/0004-6361/201526694

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

We present both the observations and the data reduction procedures of the Subaru COSMOS 20 project, an optical imaging survey of the HST COSMOS field, carried out by using Suprime-Cam on the Subaru Telescope with the following 20 optical filters: six broad-band (B, g', V, r', i', and z'), two narrow-band (NB711 and NB816), and 12 intermediate-band filters (IA427, IA464, IA484, IA505, IA527, IA574, IA624, IA679, IA709, IA738, IA767, and IA827). Part of this project is described in Taniguchi et al. (2007, ApJS, 172, 9) and Capak et al. (2007, ApJS, 172, 99) for the six broad-band and one narrow-band (NB816) filter data. In this paper, we present details of the observations and data reduction for the remaining 13 filters (the 12 IA filters and NB711). In particular, we describe the accuracy of both the photometry and astrometry in all the filter bands. We also present the optical properties of the Suprime-Cam IA filter system in appendices.

DOI： 10.1093/pasj/psv106

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

The ability to accurately derive black hole (BH) masses at progressively higher redshifts and over a wide range of continuum luminosities has become indispensable in the era of large-area extragalactic spectroscopic surveys. In this paper, we present an extension of existing comparisons between rest-frame UV and optical virial BH mass estimators to intermediate redshifts and luminosities comparable to the local Ha reverberation-mapped active galactic nuclei (AGNs). We focus on the Mg II, C IV, and C III] broad emission lines and compare them to both Ha and H beta. We use newly acquired near-infrared spectra from the Fiber-fed Multi-object Spectrograph instrument on the Subaru telescope for 89 broad-lined AGNs at redshifts between 0.3 and 3.5, complemented by data from the AGES survey. We employ two different prescriptions for measuring the emission line widths and compare the results. We confirm that Mg II shows a tight correlation with H alpha and H beta, with a scatter of similar to 0.25 dex. The C IV and C III] estimators, while showing larger scatter, are viable virial mass estimators after accounting for a trend with the UV-to-optical luminosity ratio. We find an intrinsic scatter of similar to 0.37 dex between Balmer and carbon virial estimators by combining our data set with previous high redshift measurements. This updated comparison spans a total of three decades in BH mass. We calculate a virial factor for C IV/C III] log f(C) (IV/CIII]) = 0.87 with an estimated systematic uncertainty of similar to 0.4 dex and find excellent agreement between the local reverberation mapped AGN sample and our high-z sample.

DOI： 10.1088/0004-637X/815/2/128

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Local starbursts have a higher efficiency of converting gas into stars, as compared to typical star-forming galaxies at a given stellar mass, possibly indicative of different modes of star formation. With the peak epoch of galaxy formation occurring at z &gt; 1, it remains to be established whether such an efficient mode of star formation is occurring at high redshift. To address this issue, we measure the molecular gas content of seven high-redshift (z similar to 1.6) starburst galaxies with the Atacama Large Millimeter/submillimeter Array and IRAM/Plateau de Bure Interferometer. Our targets are selected from the sample of Herschel far-infrared-detected galaxies having star formation rates (similar to 300-800 M-circle dot yr(-1)) elevated (greater than or similar to 4x) above the star-forming main sequence (MS) and included in the FMOS-COSMOS near-infrared spectroscopic survey of star-forming galaxies at z similar to 1.6 with Subaru. We detect CO emission in all cases at high levels of significance, indicative of high gas fractions (similar to 30%-50%). Even more compelling, we firmly establish with a clean and systematic selection that starbursts, identified as MS outliers, at high redshift generally have a lower ratio of CO to total infrared luminosity as compared to typical MS star-forming galaxies, although with a smaller offset than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the MS with galaxy mergers as a possible physical driver. Along with a heightened star formation efficiency, our highredshift sample is similar in other respects to local starbursts, such as being metal rich and having a higher ionization state of the interstellar medium.

DOI： 10.1088/2041-8205/812/2/L23

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

We present results from Subaru Fiber Multi Object Spectrograph near-infrared spectroscopy of 118 star-forming galaxies at z similar to 1.5 in the Subaru Deep Field. These galaxies are selected as [O II]lambda 3727 emitters at z approximate to 1.47 and 1.62 from narrow-band imaging. We detect the Ha emission line in 115 galaxies, the [O III]lambda 5007 emission line in 45 galaxies, and H beta, [N II]lambda 6584, and [S II]lambda lambda 6716, 6731 in 13, 16, and 6 galaxies, respectively. Including the [O II] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate the physical conditions of the interstellar medium in star-forming galaxies at z similar to 1.5. We find a tight correlation between Ha and [O II], which suggests that [O II] can be a good star formation rate indicator for galaxies at z similar to 1.5. The line ratios of H alpha/[O II] are consistent with those of local galaxies. We also find that [O II] emitters have strong [O III] emission lines. The [O III]/[O II] ratios are larger than normal star-forming galaxies in the local universe, suggesting a higher ionization parameter. Less massive galaxies have larger [O III]/[O II] ratios. With evidence that the electron density is consistent with local galaxies, the high ionization of galaxies athigh redshifts may be attributed to a harder radiation field by a young stellar population and/or an increase in the number of ionizing photons from each massive star.

DOI： 10.1093/pasj/psv041

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We study the ionization and kinematics of the ionized gas in the nuclear region of the barred Seyfert 2 galaxy NGC 5643 using MUSE integral field observations in the framework of the Measuring Active Galactic Nuclei Under MUSE Microscope ( MAGNUM) survey. The data were used to identify regions with different ionization conditions and to map the gas density and the dust extinction. We find evidence for a double-sided ionization cone, possibly collimated by a dusty structure surrounding the nucleus. At the center of the ionization cone, outflowing ionized gas is revealed as a blueshifted, asymmetric wing of the [OIII] emission line, up to projected velocity v(10) similar to -450 km s(-1). The outflow is also seen as a diffuse, low-luminosity radio and X-ray jet, with similar extension. The outflowing material points in the direction of two clumps characterized by prominent line emission with spectra typical of HII regions, located at the edge of the dust lane of the bar. We propose that the star formation in the clumps is due to positive feedback induced by gas compression by the nuclear outflow, providing the first candidate for outflow-induced star formation in a Seyfert-like, radio-quiet AGN. This suggests that positive feedback may be a relevant mechanism in shaping the black hole-host galaxy coevolution.

DOI： 10.1051/0004-6361/201526581

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psv057

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present a spectroscopic survey of galaxies in the COSMOS field using the Fiber Multi-object Spectrograph (FMOS), a near-infrared instrument on the Subaru Telescope. Our survey is specifically designed to detect the H alpha emission line that falls within the H-band (1.6-1.8 mu m) spectroscopic window from star-forming galaxies with 1.4 &lt; z &lt; 1.7 and M-stellar greater than or similar to 10(10) M-circle dot. With the high multiplex capability of FMOS, it is now feasible to construct samples of over 1000 galaxies having spectroscopic redshifts at epochs that were previously challenging. The high-resolution mode (R similar to 2600) effectively separates H alpha and [N II]lambda 6585, thus enabling studies of the gas-phase metallicity and photoionization state of the interstellar medium. The primary aim of our program is to establish how star formation depends on stellar mass and environment, both recognized as drivers of galaxy evolution at lower redshifts. In addition to the main galaxy sample, our target selection places priority on those detected in the far-infrared by Herschel/PACS to assess the level of obscured star formation and investigate, in detail, outliers from the star formation rate (SFR)-stellar mass relation. Galaxies with Ha detections are followed up with FMOS observations at shorter wavelengths using the J-long (1.11-1.35 mu m) grating to detect H beta and [O III]lambda 5008 which provides an assessment of the extinction required to measure SFRs not hampered by dust, and an indication of embedded active galactic nuclei. With 460 redshifts measured from 1153 spectra, we assess the performance of the instrument with respect to achieving our goals, discuss inherent biases in the sample, and detail the emission-line properties. Our higher-level data products, including catalogs and spectra, are available to the community.

DOI： 10.1088/0067-0049/220/1/12

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We report a discovery of six massive galaxies with both extremely large Ly alpha equivalent widths (EWs) and evolved stellar populations at z similar to 3. These MAssive Extremely STrong Ly alpha emitting Objects (MAESTLOs) have been discovered in our large-volume systematic survey for strong Ly alpha emitters (LAEs) with 12 optical intermediate-band data taken with Subaru/Suprime-Cam in the COSMOS field. Based on the spectral energy distribution fitting analysis for these LAEs, it is found that these MAESTLOs have (1) large rest-frame EWs of EW0 (Ly alpha) similar to 100-300 angstrom, (2) M-star similar to 10(10.5) -10(11.1) M-circle dot, and (3) relatively low specific star formation rates of SFR/M-star similar to 0.03-1 Gyr(-1). Three of the six MAESTLOs have extended Ly alpha emission with a radius of several kiloparsecs, although they show very compact morphology in the HST/ACS images, which correspond to the rest-frame UV continuum. Since the MAESTLOs do not show any evidence for active galactic nuclei, the observed extended Ly alpha emission is likely to be caused by a star formation process including the superwind activity. We suggest that this new class of LAEs, MAESTLOs, provides a missing link from star-forming to passively evolving galaxies at the peak era of the cosmic star formation history.

DOI： 10.1088/2041-8205/809/1/L7

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

Aims. Outflows driven by active galactic nuclei (AGN) are invoked by galaxy evolutionary models to quench star formation and to explain the origin of the relations observed locally between super-massive black holes and their host galaxies. We here aim to detect extended ionised outflows in luminous quasars, where we expect the highest activity both in star formation and in black-hole accretion. Currently, there are only a few studies based on spatially resolved observations of outflows at high redshift, z &gt; 2.
Methods. We analysed a sample of six luminous (L &gt; 10(47) erg/s) quasars at z similar to 2.4, observed in H-band using the near-IR integral field spectrometer SINFONI at the VLT. We performed a kinematic analysis of the [OIII] emission line at lambda = 5007 angstrom.
Results. We detect fast, spatially extended outflows in five out of six targets. [OIII]lambda 5007 has a complex gas kinematic, with blue-shifted velocities of a few hundreds of km s(-1) and line widths up to 1500 km s(-1). Using the spectroastrometric method, we infer a size of the ionised outflows of up to similar to 2 kpc. The properties of the ionised outflows, mass outflow rate, momentum rate, and kinetic power, are correlated with the AGN luminosity. The increase in outflow rate with increasing AGN luminosity is consistent with the idea that a luminous AGN pushes away the surrounding gas through fast outflows that are driven by radiation pressure, which depends on the emitted luminosity.
Conclusions. We derive mass outflow rates of about 6 700 M-circle dot yr(-1) for our sample, which are lower than those observed in molecular outflows. The physical properties of ionised outflows show dependences on AGN luminosity that are similar to those of molecular outflows, but indicate that the mass of ionised gas is lower than that of molecular outflows. Alternatively, this discrepancy between ionised and molecular outflows could be explained with different acceleration mechanisms.

DOI： 10.1051/0004-6361/201526557

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

In order to investigate the origin of quasars, we estimate the bias factor for low-luminosity quasars at high redshift for the first time. In this study, we use the two-point angular cross-correlation function (CCF) for both low-luminosity quasars at -24 &lt; M-1450 &lt; -22 and Lyman-break galaxies (LBGs). Our sample consists of both 25 low-luminosity quasars (16 objects are spectroscopically confirmed low-luminosity quasars) in the redshift range 3.1 &lt; z &lt; 4.5 and 835 color-selected LBGs with z(LBG) ' &lt; 25.0 at z similar to 4 in the COSMOS field. We have performed our analysis for the following two quasar samples: (1) the spectroscopic sample (the 16 quasars confirmed by spectroscopy), and (2) the total sample (the 25 quasars including 9 quasars with photometric redshifts). The bias factor for low-luminosity quasars at z similar to 4 is derived by utilizing the quasar-LBG CCF and the LBG auto-correlation function. We then obtain the 86% upper limits of the bias factors for low-luminosity quasars, which are 5.63 and 10.50 for the total and the spectroscopic samples, respectively. These bias factors correspond to the typical dark matter halo masses, log(M-DM/ h(-1)M(circle dot))) = 12.7 and 13.5, respectively. This result is not inconsistent with the predicted bias for quasars that is estimated by the major merger models.

DOI： 10.1088/0004-637X/809/2/138

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We present a result of a blind search for [C II] 158 μm emitters at z ̃ 4.5 using Atacama Large Millimeter Array (ALMA) Cycle 0 archival data. We collected extragalactic data covering at 330-360 GHz (band 7) from 8 Cycle 0 projects from which initial results have been already published. The total number of fields is 243 and the total on-source exposure time is 19.2 h. We searched for line emitters in continuum-subtracted data cubes with spectral resolutions of ̃50, 100, 300 and 500 km s<SUP>-1</SUP>. We could not detect any new line emitters above a 6σ significance level. This result provides upper limits to the [C II] luminosity function at z ̃ 4.5 over L_[C II] ̃ 10^8-10^{10} L_{☉} or star formation rate, SFR ̃ 10-1000 M_^{☉}yr<SUP>-1</SUP>. These limits are at least two orders of magnitude larger than the [C II] luminosity functions expected from the z ̃ 4 UV luminosity function or from numerical simulation. However, this study demonstrates that we would be able to better constrain the [C II] luminosity function and to investigate possible contributions from dusty galaxies to the cosmic star formation rate density by collecting Cycle 1+2 archival data as the ALMA Patchy Deep Survey....

DOI： 10.1093/mnras/stv1044

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We have used FMOS on Subaru to obtain near-infrared spectroscopy of 123 far-infrared-selected galaxies in COSMOS and the key rest-frame optical emission lines. This is the largest sample of infrared galaxies with near-infrared spectroscopy at these redshifts. The far-infrared selection results in a sample of galaxies that are massive systems that span a range of metallicities in comparison with previous optically selected surveys, and thus has a higher active galactic nucleus (AGN) fraction and better samples the AGN branch. We establish the presence of AGNs and starbursts in this sample of (U)LIRGs selected as Herschel-PACS and Spitzer-MIPS detections in two redshift bins (z similar to 0.7 and z similar to 1.5) and test the redshift dependence of diagnostics used to separate AGNs from star formation dominated galaxies. In addition, we construct a low-redshift (z similar to 0.1) comparison sample of infrared-selected galaxies and find that the evolution from z similar to 1.5 to today is consistent with an evolving AGN selection line and a range of ISM conditions and metallicities from the models of Kewley et al. We find that a large fraction of (U)LIRGs are BPT-selected AGNs using their new redshift-dependent classification line. We compare the position of known X-ray-detected AGNs (67 in total) with the BPT selection and find that the new classification line accurately selects most of these objects (&gt;70%). Furthermore, we identify 35 new (likely obscured) AGNs not selected as such by their X-ray emission. Our results have direct implications for AGN selection at higher redshift with either current (MOSFIRE, KMOS) or future (PFS, MOONS) spectroscopic efforts with near-infrared spectral coverage.

DOI： 10.1088/2041-8205/806/2/L35

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2041-8205/793/2/L26

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We investigate the relationships between stellar mass, gas-phase oxygen abundance (metallicity), star formation rate (SFR), and dust content of star-forming galaxies at z similar to 1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The mass-metallicity (MZ) relation at z similar to 1.6 is steeper than the relation observed in the local universe. The steeper MZ relation at z similar to 1.6 is mainly due to evolution in the stellar mass where the MZ relation begins to turnover and flatten. This turnover mass is 1.2 dex larger at z similar to 1.6. The most massive galaxies at z similar to 1.6 (similar to 10(11) M-circle dot) are enriched to the level observed in massive galaxies in the local universe. The MZ relation we measure at z similar to 1.6 supports the suggestion of an empirical upper metallicity limit that does not significantly evolve with redshift. We find an anti-correlation between metallicity and SFR for galaxies at a fixed stellar mass at z similar to 1.6, which is similar to trends observed in the local universe. We do not find a relation between stellar mass, metallicity, and SFR that is independent of redshift; rather, our data suggest that there is redshift evolution in this relation. We examine the relation between stellar mass, metallicity, and dust extinction, and find that at a fixed stellar mass, dustier galaxies tend to be more metal rich. From examination of the stellar masses, metallicities, SFRs, and dust extinctions, we conclude that stellar mass is most closely related to dust extinction.

DOI： 10.1088/0004-637X/792/1/75

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Using the first 50% of data collected for the Spitzer Large Area Survey with Hyper-Suprime-Cam observations on the 1.8 deg(2) Cosmological Evolution Survey we estimate the masses and star formation rates of 3398M(*) &gt; 10(10) M-circle dot star-forming galaxies at 4 &lt; z &lt; 6 with a substantial population up to M-* greater than or similar to 10(11.5) M-circle dot. We find that the strong correlation between stellar mass and star formation rate seen at lower redshift (the "main sequence" of star-forming galaxies) extends to z similar to 6. The observed relation and scatter is consistent with a continued increase in star formation rate at fixed mass in line with extrapolations from lower-redshift observations. It is difficult to explain this continued correlation, especially for the most massive systems, unless the most massive galaxies are forming stars near their Eddington-limited rate from their first collapse. Furthermore, we find no evidence for moderate quenching at higher masses, indicating quenching either has not occurred prior to z similar to 6 or else occurs rapidly, so that few galaxies are visible in transition between star-forming and quenched.

DOI： 10.1088/2041-8205/791/2/L25

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We present spatially resolved Atacama Large Millimeter/submillimeter Array (ALMA) [CII] observations of the z = 4.7555 submillimetre galaxy, ALESS 73.1. Our 0".5 FWHM map resolves the [CII] emitting gas which is centred close to the active galactic nucleus (AGN). The gas kinematics are dominated by rotation but with high turbulence, v(rot)/sigma(int) similar to 3.1, and a Toomre Q parameter &lt;1 throughout the disk. By fitting three independent thin rotating disk models to our data, we derive a total dynamical mass of 3 +/- 2 x 10(10) M-circle dot. This is close to the molecular gas mass derived from previous CO(2-1) observations, and implies a CO to H-2 conversion factor a(CO) &lt; 2.3 M-circle dot (K kms(-1) pc(2))(-1). The mass budget also constrains the stellar mass to &lt;3.1 x 10(10) M-circle dot, and entails a gas fraction of f(gas) greater than or similar to 0.4. The diameter of the dust continuum emission is &lt; 2 kpc, while the star-formation rate is as high as 1000 M-circle dot yr(-1). Combined with our stellar mass constraint, this implies an extreme specific star formation rate &gt;80 Gyr(-1), especially since there are no clear indications of recent merger activity. Finally, our high signal-to-noise [CII] measurement revises the observed [NII]/[CII] ratio, which suggests a close to solar metallicity, unless the [CII] flux contains significant contributions from HII regions. Our observations suggest that ALESS73.1 is a nascent galaxy undergoing its first major burst of star formation, embedded within an unstable but metal-rich gas disk.

DOI： 10.1051/0004-6361/201323331

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

DOI： 10.1088/2041-8205/785/2/L37

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We used near-infrared integral field spectroscopic observations from the AMAZE and LSD ESO programs to constrain the metallicity in a sample of 40 star-forming galaxies at 3 &lt; z &lt; 5 (most of which are at z similar to 3.4). We measured metallicities by exploiting strong emission-line diagnostics. We found that a significant fraction of star-forming galaxies at z similar to 3.4 deviate from the fundamental metallicity relation (FMR), with a metallicity of up to a factor of ten lower than expected according to the FMR. This deviation does not correlate with the dynamical properties of the galaxy or with the presence of interactions. To investigate the origin of the metallicity deviation in more detail, we also inferred information on the gas content by inverting the Schmidt-Kennicutt relation, assuming that the latter does not evolve out to z similar to 3.4. In agreement with recent CO observational data, we found that in contrast with the steeply rising trend at 0 &lt; z &lt; 2, the gas fraction in massive galaxies remains constant, with an indication of a marginal decline at 2 &lt; z &lt; 3.5. When combined with the metallicity information, we infer that to explain the low metallicity and gas content in z similar to 3.4 galaxies, both prominent outflows and massive pristine gas inflows are needed. In ten galaxies we can also spatially resolve the metallicity distribution. We found that the metallicity generally anticorrelates with the distribution of star formation and with the gas surface density. We discuss these findings in terms of pristine gas inflows toward the center, and outflows of metal-rich gas from the center toward the external regions.

DOI： 10.1051/0004-6361/201322099

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

A compact gas cloud G2 is predicted to reach the pericenter of its orbit around the supermassive black hole (SMBH) of our Galaxy, Sagittarius A*. This event will give us a rare opportunity to observe the interaction between the SMBH and the gas around it. We report on the result of a fully three-dimensional simulation of the evolution of G2 during the first pericenter passage. The strong tidal force from the SMBH stretches the cloud along its orbit, and strongly compresses it in the vertical direction, resulting in its heating up and flaring up. The bolometric luminosity will reach a maximum of similar to 100 L-circle dot. This flare should be easily observed in the near-IR.

DOI： 10.1093/pasj/pst003

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

The Subaru Prime Focus Spectrograph (PFS) is a massively multiplexed fiber-fed optical and near-infrared three-arm spectrograph (N-fiber = 2400, 380 &lt;= lambda &lt;= 1260 nm, 1 degrees.3 diameter field of view). Here, we summarize the science cases in terms of provisional plans for a 300-night Subaru survey. We describe plans to constrain the nature of dark energy via a survey of emission line galaxies spanning a comoving volume of 9.3 h(-3) Gpc(3) in the redshift range 0.8 &lt; z &lt; 2.4. In each of six redshift bins, the cosmological distances will be measured to 3% precision via the baryonic acoustic oscillation scale, and redshift-space distortion measures will constrain structure growth to 6% precision. In the near-field cosmology program, radial velocities and chemical abundances of stars in the Milky Way and M 31 will be used to infer the past assembly histories of spiral galaxies and the structure of their dark matter halos. Data will be secured for 10(6) stars in the Galactic thick-disk, halo, and tidal streams as faint as V similar to 22, including stars with V &lt; 20 to complement the goals of the Gaia mission. A medium-resolution mode with R = 5000 to be implemented in the red arm will allow the measurement of multiple alpha-element abundances and more precise velocities for Galactic stars. For the galaxy evolution program, our simulations suggest the wide wavelength range of PFS will be powerful in probing the galaxy population and its clustering over a wide redshift range. We plan to conduct a color-selected survey of 1 &lt; z &lt; 2 galaxies and AGN over 16 deg(2) to J similar or equal to 23.4, yielding a fair sample of galaxies with stellar masses above similar to 10(10) M-circle dot at z similar or equal to 2. A two-tiered survey of higher redshift Lyman break galaxies and Lyman alpha emitters will quantify the properties of early systems close to the reionization epoch.

DOI： 10.1093/pasj/pst019

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We present the first results from a near-IR spectroscopic survey of the COSMOS field, using the Fiber Multi-Object Spectrograph on the Subaru telescope, designed to characterize the star-forming galaxy population at 1.4 &lt
z &lt
1.7. The high-resolution mode is implemented to detect Hα in emission between 1.6-1.8 μm with fHα ≳ 4 × 10 -17 erg cm-2 s-1. Here, we specifically focus on 271 sBzK-selected galaxies that yield a Hα detection thus providing a redshift and emission line luminosity to establish the relation between star formation rate and stellar mass. With further J-band spectroscopy for 89 of these, the level of dust extinction is assessed by measuring the Balmer decrement using co-added spectra. We find that the extinction (0.6 ≲ A Hα ≲ 2.5) rises with stellar mass and is elevated at high masses compared to low-redshift galaxies. Using this subset of the spectroscopic sample, we further find that the differential extinction between stellar and nebular emission Estar (B-V)/Eneb(B-V) is 0.7-0.8, dissimilar to that typically seen at low redshift. After correcting for extinction, we derive an Hα-based main sequence with a slope (0.81 ± 0.04) and normalization similar to previous studies at these redshifts. © 2013. The American Astronomical Society. All rights reserved.

DOI： 10.1088/2041-8205/777/1/L8

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We performed a kinematical analysis of the [CII] line emission of the BR 1202-0725 system at z similar to 4.7 using ALMA science verification observations. The most prominent sources of this system are a quasar (QSO) and a submillimeter galaxy (SMG), separated by a projected distance of about similar to 24 kpc and characterized by very high star formation rates, higher than similar to 1000 M-circle dot yr(-1). However, the ALMA observations reveal that these galaxies apparently have undisturbed rotating disks, which is at variance with the commonly accepted scenario in which strong star formation activity is induced by a major merger. We also detected faint components which, after spectral deblending, were spatially resolved from the main QSO and SMG emissions. The relative velocities and positions of these components are compatible with orbital motions within the gravitational potentials generated by the QSO host galaxy and the SMG, suggesting that they are smaller galaxies in interaction or gas clouds in accretion flows of tidal streams. Moreover, we did not find any clear spectral evidence for outflows caused by active galactic nuclei or stellar feedback. This suggests that the high star formation rates might be induced by interactions or minor mergers with these companions, which do not affect the large-scale kinematics of the disks, however. Alternatively, the strong star formation may be fueled by the accretion of pristine gas from the host halo. Our kinematical analysis also indicates that the QSO and the SMG have similar dynamical masses, mostly in the form of molecular gas, and that the QSO host galaxy and the SMG are seen close to face-on with slightly different disk inclinations: the QSO host galaxy is seen almost face-on (i similar to 15 degrees), while the SMG is seen at higher inclinations (i similar to 25 degrees). Finally, the ratio between the black hole mass of the QSO, obtained from new X-shooter spectroscopy, and the dynamical mass of the host galaxy is similar to value found in very massive local galaxies, suggesting that the evolution of black hole galaxy relations is probably better studied with dynamical than with stellar host galaxy masses.

DOI： 10.1051/0004-6361/201322320

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

We present an investigation into how well the properties of the accretion flow on to a supermassive black hole may be coupled to those of the overlying hot corona. To do so, we specifically measure the characteristic spectral index, Gamma, of a power-law energy distribution, over an energy range of 2-10 keV, for X-ray selected, broad-lined radio-quiet active galactic nuclei (AGN) up to z similar to 2 in Cosmic Evolution Survey (COSMOS) and Extended Chandra Deep Field South (E-CDF-S). We test the previously reported dependence between Gamma and black hole mass, full width at half-maximum (FWHM) and Eddington ratio using a sample of AGN covering a broad range in these parameters based on both the Mg ii and H alpha emission lines with the later afforded by recent near-infrared spectroscopic observations using Subaru/Fibre Multi Object Spectrograph. We calculate the Eddington ratios, lambda(Edd), for sources where a bolometric luminosity (L-Bol) has been presented in the literature, based on spectral energy distribution fitting, or, for sources where these data do not exist, we calculate L-Bol using a bolometric correction to the X-ray luminosity, derived from a relationship between the bolometric correction and L-X/L-3000. From a sample of 69 X-ray bright sources (&gt; 250 counts), where Gamma can be measured with greatest precision, with an estimate of L-Bol, we find a statistically significant correlation between Gamma and lambda(Edd), which is highly significant with a chance probability of 6.59x 10(-8). A statistically significant correlation between Gamma and the FWHM of the optical lines is confirmed, but at lower significance than with lambda(Edd) indicating that lambda(Edd) is the key parameter driving conditions in the corona. Linear regression analysis reveals that Gamma = (0.32 +/- 0.05) log(10)lambda(Edd) + (2.27 +/- 0.06) and Gamma = (-0.69 +/- 0.11) log(10)(FWHM/km s(-1)) + (4.44 +/- 0.42). Our results on Gamma-lambda(Edd) are in very good agreement with previous results. While the Gamma-lambda(Edd) relationship means that X-ray spectroscopy may be used to estimate black hole accretion rate, considerable dispersion in the correlation does not make this viable for single sources, however could be valuable for large X-ray spectral samples, such as those to be produced by eROSITA.

DOI： 10.1093/mnras/stt920

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present an analysis of broad emission lines observed in moderate-luminosity active galactic nuclei (AGNs), typical of those found in X-ray surveys of deep fields, with the goal of testing the validity of single-epoch virial black hole mass estimates. We have acquired near-infrared spectra of AGNs up to z similar to 1.8 in the COSMOS and Extended Chandra Deep Field-South Survey, with the Fiber Multi-Object Spectrograph mounted on the Subaru telescope. These near-infrared spectra provide a significant detection of the broad H alpha line, shown to be a reliable probe of black hole mass at low redshift. Our sample has existing optical spectroscopy that provides a detection of Mg II, typically used for black hole mass estimation at z greater than or similar to 1. We carry out a spectral-line fitting procedure using both H alpha and Mg II to determine the virial velocity of gas in the broad-line region, the continuum luminosity at 3000 angstrom, and the total H alpha line luminosity. With a sample of 43 AGNs spanning a range of two decades in luminosity, we find a tight correlation between the ultraviolet and emission-line luminosity. There is also a close one-to-one relationship between the full width at half-maximum of H alpha and Mg II. Both of these then lead to there being very good agreement between H alpha- and Mg II-based masses over a wide range in black hole mass, i.e., M-BH similar to 10(7-9) M-circle dot. In general, these results demonstrate that local scaling relations, using Mg II or H alpha, are applicable for AGNs at moderate luminosities and up to z similar to 2.

DOI： 10.1088/0004-637X/771/1/64

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We investigated the fraction of [OII] emitters in galaxies at z similar to 0.9 as a function of the local galaxy density in the Hubble Space Telescope (HST) COSMOS 2 deg(2) field. [OII] emitters are selected by the narrowband excess technique with the NB711-band imaging data taken with Suprime-Cam on the Subaru telescope. We carefully selected 614 photo-z-selected galaxies with M-U3500 &lt; -19.31 at z = 0.901 - 0.920, which includes 195 [OII] emitters, to directly compare the results with our previous study at z similar to 1.2. We found that the fraction is almost constant at 0.3 Mpc (2) &lt; Sigma(10th) &lt; 10 Mpc (2). We also checked the fraction of galaxies with blue rest-frame colors of NUV - R &lt; 2 in our photo-z-selected sample, and found that the fraction of blue galaxies does not significantly depend on the local density. On the other hand, the semi-analytic model of galaxy formation predicted that the fraction of star-forming galaxies at z similar to 0.9 decreases with increasing projected galaxy density even if the effects of the projection and the photo-z error in our analysis were taken into account. The fraction of [OII] emitters decreases from similar to 60% at z similar to 1.2 to similar to 30% at z similar to 0.9 independent of galaxy environment. The decrease of the [OII] emitter fraction could be explained mainly by the rapid decrease of star formation activity in the universe from z similar to 1.2 to z similar to 0.9.

DOI： 10.1088/0004-637X/768/1/51

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We investigate the chemical properties of low-z QSOs, using archival UV spectra obtained with the Hubble Space Telescope and International Ultraviolet Explorer for a sample of 70 Palomar-Green QSOs at z &lt; 0.5. By utilizing the flux ratios of UV emission lines (i.e., N V/C IV, (Si IV+O IV])/C IV, and N V/He II) as metallicity indicators, we compare broad-line region (BLR) gas metallicity with active galactic nucleus (AGN) properties, i.e., black hole (BH) mass, luminosity, and Eddington ratio. We find that BLR metallicity correlates with Eddington ratio while the dependency on BH mass is much weaker. Although these trends of low-z AGNs appear to be different from those of high-z QSOs, the difference between low-z and high-z samples is partly caused by the limited dynamical range of the samples. We find that metal enrichment at the center of galaxies is closely connected to the accretion activity of BHs and that the scatter of metallicity correlations with BH mass increases over cosmic time.

DOI： 10.1088/0004-637X/763/1/58

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

The M82 "cap" is a gas cloud at a projected radius of 11.6 kpc along the minor axis of this well-known superwind source. The cap has been detected in optical line emission and X-ray emission and therefore provides an important probe of the wind energetics. In order to investigate the ionization source of the cap, we observed it with the Kyoto3DII Fabry-Perot instrument mounted on the Subaru Telescope. Deep continuum, H alpha, [NII]lambda 6583/H alpha, and [S II]lambda lambda 6716,6731/H alpha maps were obtained with subarcsecond resolution. The superior spatial resolution compared to earlier studies reveals a number of bright H alpha emitting clouds within the cap. The emission line widths (less than or similar to 100 km s(-1) FWHM) and line ratios in the newly identified knots are most reasonably explained by slow to moderate shocks velocities (v(shock) = 40-80 km s(-1)) driven by a fast wind into dense clouds. The momentum input from the M82 nuclear starburst region is enough to produce the observed shock. Consequently, earlier claims of photoionization by the central starburst are ruled out because they cannot explain the observed fluxes of the densest knots unless the UV escape fraction is very high (f(esc) &gt; 60%), i.e., an order of magnitude higher than observed in dwarf galaxies to date. Using these results, we discuss the evolutionary history of the M82 superwind. Future UV/X-ray surveys are expected to confirm that the temperature of the gas is consistent with our moderate shock model.

DOI： 10.1088/0004-637X/761/1/55

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We have identified a very interesting Ly alpha emitter (LAE), whose Ly alpha emission line has an extremely large observed equivalent width of EW0 = 436(-149)(+422) angstrom, which corresponds to an extraordinarily large intrinsic rest-frame equivalent width of EW0int = 872(-298)(+844) angstrom after the average intergalactic absorption correction. The object was spectroscopically confirmed to be a real LAE by its apparent asymmetric Ly alpha line profile detected at z = 6.538. The continuum emission of the object was definitely detected in our deep z'-band image; thus, its EW0 was reliably determined. Follow-up deep near-infrared spectroscopy revealed emission lines of neither He II lambda 1640 as an apparent signature of Population III (Pop III) nor C IV lambda 1549 as proof of an active nucleus. No detection of the short-lived He II lambda 1640 line is not necessarily inconsistent with the interpretation that the underlying stellar population of the object is dominated by Pop III. We found that the observed extremely large EW0 of the Ly alpha emission and the upper limit on the EW0 of the He II lambda 1640 emission can be explained by population synthesis models favoring a very young age less than 2-4 Myr and massive metal-poor (Z &lt; 10(-5)) or even metal-free stars. The observed large EW0 of Ly alpha is insufficiently explained by Population I/II synthesis models with Z &gt;= 10(-3). However, we cannot conclusively rule out the possibility that this object is composed of a normal stellar population with a clumpy dust distribution, which could enhance the Ly alpha EW0, though its significance is still unclear.

DOI： 10.1088/0004-637X/761/2/85

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Young radio galaxies (YRGs) provide an ideal laboratory to explore the connection between the accretion disk and radio jet thanks to their recent jet formation. We investigate the relationship between the emission-line properties, the black hole accretion rate, and the radio properties using a sample of 34 low-redshift (z &lt; 0.4) YRGs. We classify YRGs as high-excitation galaxies (HEGs) and low-excitation galaxies (LEGs) based on the flux ratio of high-ionization to low-ionization emission lines. Using the H alpha luminosities as a proxy of accretion rate, we find that HEGs in YRGs have similar to 1 dex higher Eddington ratios than LEGs in YRGs, suggesting that HEGs have a higher mass accretion rate or higher radiative efficiency than LEGs. In agreement with previous studies, we find that the luminosities of emission lines, in particular H alpha, are correlated with radio core luminosity, suggesting that accretion and young radio activities are fundamentally connected.

DOI： 10.1088/0004-637X/757/2/140

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present the result of our low-luminosity quasar survey in the redshift range of 4.5 less than or similar to z less than or similar to 5.5 in the COSMOS field. Using the COSMOS photometric catalog, we selected 15 quasar candidates with 22 &lt; i' &lt; 24 at z similar to 5 that are similar to 3 mag fainter than the Sloan Digital Sky Survey quasars in the same redshift range. We obtained optical spectra for 14 of the 15 candidates using FOCAS on the Subaru Telescope and did not identify any low-luminosity type-1 quasars at z similar to 5, while a low-luminosity type-2 quasar at z similar to 5.07 was discovered. In order to constrain the faint end of the quasar luminosity function at z similar to 5, we calculated the 1 sigma confidence upper limits of the space density of type-1 quasars. As a result, the 1 sigma confidence upper limits on the quasar space density are Phi &lt; 1.33 x 10(-7) Mpc(-3) mag(-1) for -24.52 &lt; M-1450 &lt; -23.52 and Phi &lt; 2.88 x 10(-7) Mpc(-3) mag(-1) for -23.52 &lt; M-1450 &lt; -22.52. The inferred 1s confidence upper limits of the space density are then used to provide constraints on the faint-end slope and the break absolute magnitude of the quasar luminosity function at z similar to 5. We find that the quasar space density decreases gradually as a function of redshift at low luminosity (M-1450 similar to -23), being similar to the trend found for quasars with high luminosity (M-1450 &lt; -26). This result is consistent with the so-called downsizing evolution of quasars seen at lower redshifts.

DOI： 10.1088/0004-637X/756/2/160

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present the first detailed study of the stellar populations of star-forming galaxies at z similar to 1.5, which are selected by their [O II] emission line, detected in narrowband surveys. We identified similar to 1300 [O II] emitters at z = 1.47 and z = 1.62 in the Subaru Deep Field with rest-frame equivalent widths (EWs) above 13 angstrom. Optical and near-infrared spectroscopic observations for approximate to 10% of our samples show that our separation of [O II] from [O III] emission-line galaxies in two-color space is 99% successful. We analyze the multi-wavelength properties of a subset of similar to 1200 galaxies with the best photometry. They have average rest-frame EW of 45 angstrom, stellar mass of 3 x 10(9) M-circle dot, and stellar age of 100 Myr. In addition, our spectral energy distribution (SED) fitting and broadband colors indicate that [O II] emitters span the full range of galaxy populations at z similar to 1.5. We also find that 80% of [O II] emitters are also photometrically classified as "BX/BM" (UV) galaxies and/or the star-forming "BzK" (near-IR) galaxies. Our [O II] emission line survey produces a far more complete and somewhat deeper sample of z similar to 1.5 galaxies than either the BX/BM or sBzK selection alone. We constructed average SEDs and find that higher [O II] EW galaxies have somewhat bluer continua. SED model-fitting shows that they have on average half the stellar mass of galaxies with lower [O II] EW. The observed [O II] luminosity is well correlated with the far-UV continuum with a logarithmic slope of 0.89 +/- 0.22. The scatter of the [O II] luminosity against the far-UV continuum suggests that [O II] can be used as a star formation rate indicator with a reliability of 0.23 dex.

DOI： 10.1088/0004-637X/757/1/63

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We investigate the high-redshift quasar luminosity function (QLF) down to an apparent magnitude of I-AB = 25 in the Cosmic Evolution Survey (COSMOS). Careful analysis of the extensive COSMOS photometry and imaging data allows us to identify and remove stellar and low-redshift contaminants, enabling a selection that is nearly complete for type-1 quasars at the redshifts of interest. We find 155 likely quasars at z &gt; 3.1, 39 of which have prior spectroscopic confirmation. We present our sample in detail and use these confirmed and likely quasars to compute the rest-frame UV QLF in the redshift bins 3.1 &lt; z &lt; 3.5 and 3.5 &lt; z &lt; 5. The space density of faint quasars decreases by roughly a factor of four from z similar to 3.2 to z similar to 4, with faint-end slopes of beta similar to -1.7 at both redshifts. The decline in space density of faint optical quasars at z &gt; 3 is similar to what has been found for more luminous optical and X-ray quasars. We compare the rest-frame UV luminosity functions found here with the X-ray luminosity function at z &gt; 3, and find that they evolve similarly between z similar to 3.2 and z similar to 4; however, the different normalizations imply that roughly 75% of X-ray bright active galactic nuclei (AGNs) at z similar to 3-4 are optically obscured. This fraction is higher than found at lower redshift and may imply that the obscured, type-2 fraction continues to increase with redshift at least to z similar to 4. Finally, the implications of the results derived here for the contribution of quasars to cosmic reionization are discussed.

DOI： 10.1088/0004-637X/755/2/169

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We present near-infrared spectroscopy of the z similar or equal to 3.2 quasar SDSS J1707+6443, obtained with MOIRCS on the Subaru Telescope. This quasar is classified as a "nitrogen-loud" quasar because of the fairly strong N III] and N IV] semi-forbidden emission lines from the broad-line region (BLR) observed in its rest-frame UV spectrum. However, our rest-frame optical spectrum from MOIRCS shows strong [O III] emission from the narrow-line region (NLR), suggesting that, at variance with the BLR, NLR gas is not metal-rich. To reconcile these contradictory results, there may be two alternative possibilities: (1) the strong nitrogen lines from the BLR are simply caused by a very high relative abundance of nitrogen and not by a very high BLR metallicity, or (2) the BLR metallicity is not representative of the metallicity of the host galaxy, which is better traced by the NLR. In either case, the strong broad nitrogen lines in the UV spectrum are ot indication of a chemically enriched host galaxy. We estimated the black hole mass and Eddington ratio of this quasar from the velocity width of both C IV and H beta, which results in log(M-BH/M-circle dot) = 9.50 and log(L-bol/L-Edd) = -0.34. The relatively high Eddington ratio is consistent with our earlier result that strong nitrogen emission from BLRs is associated with high Eddington ratios. Finally, we detected significant [Ne III] emission from the NLR, implying a quite high gas density of n(e) similar to 10(6) cm(-3) and suggesting a strong coupling between quasar activity and dense interstellar clouds in the host galaxy.

DOI： 10.1051/0004-6361/201118477

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present our new deep optical imaging and long-slit spectroscopy for Arp 220, the archetypical ultra luminous infrared galaxy in the local universe. Our sensitive H alpha imaging has newly revealed large-scale H alpha absorption, i.e., post-starburst regions in this merger. One is found in the eastern superbubble and the other is in the two tidal tails that are clearly revealed in our deep optical imaging. The size of the H alpha absorption region in the eastern bubble is 5 kpc x 7.5 kpc, and the observed H alpha equivalent widths are similar to 2 angstrom +/- 0.2 angstrom. The sizes of the northern and southern H alpha-absorption tidal tails are similar to 5 kpc x 10 kpc and similar to 6 kpc x 20 kpc, respectively. The observed H alpha equivalent widths range from 4 angstrom to 7 angstrom. In order to explain the presence of the two post-starburst tails, we suggest a possible multiple-merger scenario for Arp 220 in which two post-starburst disk-like structures merged into one, causing the two tails. This favors Arp 220 as a multiple merging system composed of four or more galaxies arising from a compact group of galaxies. Taking our new results into account, we discuss a star formation history in the last 1 Gyr in Arp 220.

DOI： 10.1088/0004-637X/753/1/78

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We present one of the first resolved maps of the [CII] 158 mu m line, a powerful tracer of the star forming inter-stellar medium, at high redshift. We use the new IRAM PdBI receivers at 350 GHz to map this line in BRI 0952-0115, the host galaxy of a lensed quasar at z = 4.4 previously found to be very bright in [CII] emission. The [CII] emission is clearly resolved and our data allow us to resolve two [CII] lensed images associated with the optical quasar images. We find that the star formation, as traced by [CII], is distributed over a region of about 1 kpc in size near the quasar nucleus, and we infer a star formation surface density greater than or similar to 150 M-circle dot yr(-1) kpc(-2), similar to that observed in local ULIRGs. We also reveal another [CII] component, extended over similar to 12 kpc, and located at about 10 kpc from the quasar. We suggest that this component is a companion disk galaxy, in the process of merging with the quasar host, whose rotation field is distorted by the interaction with the quasar host, and where star formation, although intense, is more diffuse. These observations suggest that galaxy merging at high-z can enhance star formation at the same time in the form of more compact regions, in the vicinity of the accreting black hole, and in more extended star forming galaxies.

DOI： 10.1051/0004-6361/201118705

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/201219518

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We report the discovery of a protocluster at z similar to 6 containing at least eight cluster member galaxies with spectroscopic confirmations in the wide-field image of the Subaru Deep Field (SDF). The overdensity of the protocluster is significant at the 6 sigma level, based on the surface number density of i'-dropout galaxies. The overdense region covers similar to 6' x 6' (14 Mpc x 14 Mpc in comoving units at z = 6) and includes 30 i'-dropout galaxies. Follow-up spectroscopy revealed that 15 of these are real z similar to 6 galaxies (5.7 &lt; z &lt; 6.3). Of these 15, 8 are clustering in a narrow redshift range (Delta z &lt; 0.05 centered at z = 6.01), corresponding to a seven-fold increase in number density over the average in redshift space. We found no significant difference in the observed properties, such as Ly alpha luminosities and UV continuum magnitudes, between the eight protocluster members and the seven non-members. The velocity dispersion of the eight protocluster members is 647 +/- 124 km s(-1), which is about three times higher than that predicted by the standard cold dark matter model. This discrepancy could be attributed to the distinguishing three-dimensional distribution of the eight protocluster members. We discuss two possible explanations for this discrepancy: either the protocluster is already mature, with old galaxies at the center, or it is still immature and composed of three subgroups merging to become a larger cluster. In either case, this concentration of z = 6.01 galaxies in the SDF may be one of the first sites of formation of a galaxy cluster in the universe.

DOI： 10.1088/0004-637X/750/2/137

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

The success of future large-scale weak-lensing surveys will critically depend on the accurate estimation of photometric redshifts of very large samples of galaxies. This in turn depends on both the quality of the photometric data and the photo-z estimators. In a previous study, we focused primarily on the impact of photometric quality on photo-z estimates and on the development of novel techniques to construct the N(z) of tomographic bins at the high level of precision required for precision cosmology, as well as the correction of issues such as imprecise corrections for Galactic reddening. We used the same set of templates to generate the simulated photometry as were then used in the photo-z code, thereby removing any effects of 'template error'. In this work we now include the effects of 'template error' by generating simulated photometric data set from actual COSMOS photometry. We use the trick of simulating redder photometry of galaxies at higher redshifts by using a bluer set of passbands on low-z galaxies with known redshifts. We find that 'template error' is a rather small factor in photo-z performance, at the photometric precision and filter complement expected for all-sky surveys. With only a small subset of training galaxies with spectroscopic redshifts, it is in principle possible to construct tomographic redshift bins whose mean redshift is known, from photo-z alone, to the required accuracy of vertical bar Delta(&lt; z &gt;)vertical bar &lt;= 0.002(1 + z).

DOI： 10.1111/j.1365-2966.2012.20427.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

In order to understand environmental effects on star formation in high-redshift galaxies, we investigate the physical relationships between the star formation activity, stellar mass, and environment for z similar or equal to 1.2 galaxies in the 2 deg(2) COSMOS field. We estimate star formation using the [O II]lambda 3727 emission line and environment from the local galaxy density. Our analysis shows that for massive galaxies (M-* greater than or similar to 10(10) M-circle dot), the fraction of [O II] emitters in high-density environments (Sigma(10th) greater than or similar to 3.9 Mpc(-2)) is 1.7 +/- 0.4 times higher than in low-density environments (Sigma(10th) less than or similar to 1.5 Mpc(-2)), while the [O II] emitter fraction does not depend on environment for low-mass M-* less than or similar to 10(10) M-circle dot galaxies. In order to understand what drives these trends, we investigate the role of companion galaxies in our sample. We find that the fraction of [O II] emitters in galaxies with companions is 2.4 +/- 0.5 times as high as that in galaxies without companions at M-* greater than or similar to 10(10) M-circle dot. In addition, massive galaxies are more likely to have companions in high-density environments. However, although the number of star-forming galaxies increases for massive galaxies with close companions and in dense environments, the average star formation rate of star-forming galaxies at a given mass is independent of environment and the presence/absence of a close companion. These results suggest that interactions and/or mergers in a high-density environment could induce star formation in massive galaxies at z similar to 1.2, increasing the fraction of star-forming galaxies with M-* greater than or similar to 10(10) M-circle dot.

DOI： 10.1088/0004-637X/747/1/42

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

The stellar metallicity is a direct measure of the amount of metals present in a galaxy, since a large part of the metals lie in its stars. In this paper, we investigate new stellar metallicity indicators suitable for high-z galaxies by studying the stellar photospheric absorption lines in the rest-frame ultraviolet, hence sampling predominantly young hot stars. We defined these new indicators based on the equivalent widths (EW) of selected features using theoretical spectra created with the evolutionary population synthesis code Starburst99. We used them to compute the stellar metallicity for a sample of ultraviolet-selected galaxies at z &gt; 3 from the AMAZE (Assessing the Mass-Abundance redshift Evolution) survey using very deep (37 h per object) VLT/FORS spectra. Moreover, we applied these new metallicity indicators to eight additional high redshift galaxies studied in literature. We then compared stellar and gas-phase metallicities measured from the emission lines for all these galaxies, finding that within the errors the two estimates are in good agreement, with possible tendency for stellar metallicities to be lower than the gas phase ones. For the first time, we study the stellar mass-stellar metallicity relation at z &gt; 3. We find that the metallicity of young, hot stars in galaxies at z similar to 3 have similar values of the aged stars in local SDSS galaxies, in contrast to findings for the gas phase metallicity.

DOI： 10.1051/0004-6361/201118134

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/742/2/61

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present Keck spectroscopic observations of z &gt; 6 Lyman-break galaxy (LBG) candidates in the Subaru Deep Field (SDF). The candidates were selected as i'-dropout objects down to z' = 27 AB magnitudes from an ultra-deep SDF z'-band image. With the Keck spectroscopy we identified 19 LBGs with prominent Ly alpha emission lines at 6 &lt;= z &lt;= 6.4. The median value of the Ly alpha rest-frame equivalent widths (EWs) is similar to 50 angstrom, with four EWs &gt; 100 angstrom. This well-defined spectroscopic sample spans a UV-continuum luminosity range of -21.8 &lt;= M-UV &lt;= -19.5 (0.6 similar to 5 L-UV*) and a Ly alpha luminosity range of (0.3-3) x 10(43) erg s(-1) (0.3-3 L-Ly alpha*). We derive the UV and Ly alpha luminosity functions (LFs) from our sample at &lt; z &gt; similar to 6.2 after we correct for sample incompleteness. We find that our measurement of the UV LF is consistent with the results of previous studies based on photometric LBG samples at 5 &lt; z &lt; 7. Our Ly alpha LF is also generally in agreement with the results of Ly alpha-emitter surveys at z similar to 5.7 and 6.6. This study shows that deep spectroscopic observations of LBGs can provide unique constraints on both the UV and Ly alpha LFs at z &gt; 6.

DOI： 10.1088/0004-637X/743/1/65

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We present a deep optical spectrum of TN J0924-2201, the most distant radio galaxy at z = 5.19, obtained with FOCAS on the Subaru Telescope. We successfully detect, for the first time, the CIV lambda 1549 emission line from the narrow-line region. In addition to the emission-line fluxes of Ly alpha and CIV, we set upper limits on the NV and HeII emissions. We use these line detections and upper limits to constrain the chemical properties of TN J0924-2201. By comparing the observed emission-line flux ratios with photoionization models, we infer that the carbon-to-oxygen relative abundance is already [C/O] &gt; -0.5 at a cosmic age of similar to 1.1 Gyr. This lower limit on [C/O] is higher than the ratio expected at the earliest phases of the galaxy chemical evolution, indicating that TN J0924-2201 has already experienced significant chemical evolution at z = 5.19.

DOI： 10.1051/0004-6361/201117641

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Several UV and near-infrared color selection methods have identified galaxies at z = 1-3. Since each method suffers from selection biases, we have simultaneously applied three leading techniques (Lyman break, BX/BM, and BzK selection) in the Subaru Deep Field. This field has reliable (Delta z/(1 + z) = 0.02-0.09) photometric redshifts for similar to 53,000 galaxies from 20 bands (1500 angstrom-2.2 mu m). The BzK, LBG, and BX/BM samples suffer contamination from z &lt; 1 interlopers of 6%, 8%, and 20%, respectively. Around the redshifts where it is most sensitive (z similar to 1.9 for star-forming BzK, z similar to 1.8 for z similar to 2 LBGs, z similar to 1.6 for BM, and z similar to 2.3 for BX), each technique finds 60%-80% of the census of the three methods. In addition, each of the color techniques shares 75%-96% of its galaxies with another method, which is consistent with previous studies that adopt identical criteria on magnitudes and colors. Combining the three samples gives a comprehensive census that includes approximate to 90% of z(phot) = 1-3 galaxies, using standard magnitude limits similar to previous studies. In fact, we find that among z = 1-2.5 galaxies in the color selection census, 81%-90% of them can be selected by just combining the BzK selection with one of the UV techniques (z similar to 2 LBG or BX and BM). The average galaxy stellar mass, reddening, and star formation rates (SFRs) all decrease systematically from the sBzK population to the LBGs, and to the BX/BMs. The combined color selections yield a total cosmic SFR density of 0.18 +/- 0.03 M-circle dot yr(-1) Mpc(-3) for K-AB less than or similar to 24. We find that 65% of the star formation is in galaxies with E(B - V) &gt; 0.25 mag, even though they are only one-fourth of the census by number.

DOI： 10.1088/0004-637X/735/2/91

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We present the detection of bright [CII] emission in the z = 4.76 submillimetre galaxy LESS J033229.4-275619 using the Atacama Pathfinder EXperiment. This represents the highest redshift [CII] detection in a submm selected, star-formation dominated system. The AGN contributions to the [CII] and far-infrared (FIR) luminosities are small. We find an atomic mass derived from [CII] comparable to the molecular mass derived from CO. The ratio of the [CII], CO and FIR luminosities imply a radiation field strength G(0) similar to 10(3) and a density similar to 10(4) cm(-3) in a kpc-scale starburst, as seen in local and high redshift starbursts. The high L-[CII]/L-FIR = 2.4x10(-3) and the very high L-[CII]/LCO(1-0) approximate to 10(4) are reminiscent of low metallicity dwarf galaxies, suggesting that the highest redshift star-forming galaxies may also be characterised by lower metallicities. We discuss the implications of a reduced metallicity on studies of the gas reservoirs, and conclude that especially at very high redshift, [CII] may be a more powerful and reliable tracer of the interstellar matter than

DOI： 10.1051/0004-6361/201116868

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We carried out extended spectroscopic confirmations of Ly alpha emitters (LAEs) at z = 6.5 and 5.7 in the Subaru Deep Field. Now, the total number of spectroscopically confirmed LAEs is 45 and 54 at z = 6.5 and 5.7, respectively, and at least 81% (70%) of our photometric candidates at z = 6.5 (5.7) have been spectroscopically identified as real LAEs. We made careful measurements of the Ly alpha luminosity, both photometrically and spectroscopically, to accurately determine the Ly alpha and rest-UV luminosity functions (LFs). The substantially improved evaluation of the Ly alpha LF at z = 6.5 shows an apparent deficit from z = 5.7 at least at the bright end, and a possible decline even at the faint end, though small uncertainties remain. The rest-UV LFs at z = 6.5 and 5.7 are in good agreement, at least at the bright end, in clear contrast to the differences seen in the Ly alpha LF. These results imply an increase in the neutral fraction of the intergalactic medium from z = 5.7 to 6.5. The rest-frame equivalent width (EW0) distribution at z = 6.5 seems to be systematically smaller than z = 5.7, and it shows an extended tail toward larger EW0. The bright end of the rest-UV LF can be reproduced from the observed Ly alpha LF and a reasonable EW0-UV luminosity relation. Integrating this rest-UV LF provides the first measurement of the contribution of LAEs to the photon budget required for reionization. The derived UV LF suggests that the fractional contribution of LAEs to the photon budget among Lyman break galaxies significantly increases toward faint magnitudes. Low-luminosity LAEs could dominate the ionizing photon budget, though this inference depends strongly on the uncertain faint-end slope of the Ly alpha LF.

DOI： 10.1088/0004-637X/734/2/119

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We show how accretion rate governs the physical properties of a sample of unobscured broad-line, narrow-line, and lineless active galactic nuclei (AGNs). We avoid the systematic errors plaguing previous studies of AGN accretion rates by using accurate intrinsic accretion luminosities (L-int) from well-sampled multiwavelength spectral energy distributions from the Cosmic Evolution Survey, and accurate black hole masses derived from virial scaling relations (for broad-line AGNs) or host-AGN relations (for narrow-line and lineless AGNs). In general, broad emission lines are present only at the highest accretion rates (L-int/L-Edd &gt; 10(-2)), and these rapidly accreting AGNs are observed as broad-line AGNs or possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower specific accretion rates (L-int/L-Edd &lt; 10(-2)) are unobscured and yet lack a broad-line region. The disappearance of the broad emission lines is caused by an expanding radiatively inefficient accretion flow (RIAF) at the inner radius of the accretion disk. The presence of the RIAF also drives L-int/L-Edd &lt; 10(-2) narrow-line and lineless AGNs to have ratios of radio-to-optical/UV emission that are 10 times higher than L-int/L-Edd &gt; 10(-2) broad-line AGNs, since the unbound nature of the RIAF means it is easier to form a radio outflow. The IR torus signature also tends to become weaker or disappear from L-int/L-Edd &lt; 10(-2) AGNs, although there may be additional mid-IR synchrotron emission associated with the RIAF. Together, these results suggest that specific accretion rate is an important physical "axis" of AGN unification, as described by a simple model.

DOI： 10.1088/0004-637X/733/1/60

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present Subaru/FOCAS spectropolarimetry of two active galaxies in the Cosmic Evolution Survey. These objects were selected to be optically dull, with the bright X-ray emission of an active galactic nucleus (AGN) but missing optical emission lines in our previous spectroscopy. Our new observations show that one target has very weak emission lines consistent with an optically dull AGN, while the other object has strong emission lines typical of a host-diluted Type 2 Seyfert galaxy. In neither source do we observe polarized emission lines, with 3 sigma upper limits of P-BLR less than or similar to 2%. This means that the missing broad emission lines (and weaker narrow emission lines) are not due to simple anisotropic obscuration, e. g., by the canonical AGN torus. The weak-lined optically dull AGN exhibits a blue polarized continuum with P = 0.78% +/- 0.07% at 4400 angstrom &lt; lambda(rest) &lt; 7200 angstrom (P = 1.37% +/- 0.16% at 4400 angstrom &lt; lambda(rest) &lt; 5050 angstrom). The wavelength dependence of this polarized flux is similar to that of an unobscured AGN continuum and represents the intrinsic AGN emission, either as synchrotron emission or the outer part of an accretion disk reflected by a clumpy dust scatterer. Because this intrinsic AGN emission lacks emission lines, this source is likely to have a radiatively inefficient accretion flow.

DOI： 10.1088/0004-637X/732/1/23

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We present a SINFONI integral-field kinematical study of 33 galaxies at z similar to 3 from the AMAZE and LSD projects, which are aimed at studying metallicity and dynamics of high-redshift galaxies. The number of galaxies analyzed in this paper constitutes a significant improvement over existing data in the literature, and this is the first time that a dynamical analysis is obtained for a relatively large sample of galaxies at z similar to 3. Eleven galaxies show ordered rotational motions (similar to 30% of the sample). In these cases we estimate dynamical masses by modeling the gas kinematics with rotating disks and exponential mass distributions. We find dynamical masses in the range 2 x 10(9) M-circle dot-2 x 10(11) M-circle dot with a mean value of similar to 2 x 10(10) M-circle dot. By comparing observed gas velocity dispersion with what is expected from models, we find that most rotating objects are dynamically "hot", with intrinsic velocity dispersions of similar to 90 km s(-1). The median value of the ratio between the maximum disk rotational velocity and the intrinsic velocity dispersion for the rotating objects is 1.6, much lower than observed in local galaxies value (similar to 10) and slightly lower than the z similar to 2 value (2-4). Finally we use the maximum rotational velocity from our modeling to build a baryonic Tully-Fisher relation at z similar to 3. Our measurements indicate that z similar to 3 galaxies have lower stellar masses (by a factor of ten on average) compared to local galaxies with the same dynamical mass. However, the large observed scatter suggests that the Tully-Fisher relation is not yet "in place" at these early cosmic ages, possibly owing to the young age of galaxies. A smaller dispersion of the Tully-Fisher relation is obtained by taking the velocity dispersion into account with the use of the S-0.5 indicator, suggesting that turbulent motions might play an important dynamical role.

DOI： 10.1051/0004-6361/201015465

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

Active galactic nuclei (AGNs) are characterized by a clear correlation between luminosity and metallicity (L-AGN-Z(AGN) relation). The origin of this correlation is not clear. It may result from a relation between the black hole mass (M-BH) and metallicity, or from a relation between the accretion rate (L/L-Edd) and metallicity. To investigate the origin of the L-AGN-Z(AGN) relation, we use optical spectra of 2383 quasars at 2.3 &lt; z &lt; 3.0 from the Sloan Digital Sky Survey. By using this data set, we constructed composite spectra of 33 subsamples in intervals of both MBH and L/LEdd. From these composite spectra we measured emission-line flux ratios that are sensitive to the metallicity of the broad line region (BLR): specifically, N V lambda 1240/C IV lambda 1549, N V lambda 1240/He II lambda 1640, (Si IV lambda 1398+O IV]lambda 1402)/C IV lambda 1549, and Al III lambda 1857/C IV lambda 1549. We find that there is a significant correlation between M-BH and Z(BLR) as inferred from all four metallicity-sensitive emission-line flux ratios. This result strongly suggests that the observed L-AGN-Z(AGN) relation is mostly a consequence of the M-BH-Z(AGN) relation. The relation between M-BH and Z(BLR) is likely a consequence of both the M-BH-M-bul relation and of the mass-metallicity relation in the host galaxy. We also find that L/L-Edd correlates with the emission line flux ratios involving N V (more specifically, N V/C IV and N V/He II), while it does not correlate with the other two metallicity sensitive emission line flux ratios, i.e., (Si IV+ O IV])/C IV and Al III/C IV. These correlations indicate that the emission-line flux ratios involving N V depend on both the metallicity and relative abundance of nitrogen. We suggest that the relation between L/L-Edd and those line ratios involving nitrogen is caused by a delay of the black hole accretion rate relative to the onset of nuclear star formation of about 108 years, which is the timescale required for the nitrogen enrichment.

DOI： 10.1051/0004-6361/201015584

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

We present J-band long-slit spectroscopic observation of NGC 1068 classified as a Seyfert 2 galaxy. J-band observations with OAO/ISLE provide clear detection of spatially extended [Fe II] 1.257 mu m and [P II] 1.188 mu m lines. We found that [Fe II] 1.257 mu m/[P II] 1.188 mu M increases with distance from a central continuum peak. Observed line ratios around the nucleus (continuum peak) are consistent with a typical value expected from photoionization models, while the ratios at 3"-4" (210-280 pc) east and west of the nucleus are slightly higher than this. In the off nucleus region of NGC 1068 we also found a possible association between [Fe II] 1.257 mu m/[P II] 1.188 mu m and the radio continuum. This suggests a mild contribution of shock ionization induced by a radio jet outside nucleus while photoionization by the central energy source is dominant near the nucleus.

DOI： 10.1093/pasj/63.1.L7

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/201015471

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We searched for quasars that are similar to 3 mag fainter than the SDSS quasars in the redshift range 3.7 less than or similar to z less than or similar to 4.7 in the COSMOS field to constrain the faint end of the quasar luminosity function (QLF). Using optical photometric data, we selected 31 quasar candidates with 22 &lt; i' &lt; 24 at z similar to 4. We obtained optical spectra for most of these candidates using FOCAS on the Subaru telescope and identified eight low-luminosity quasars at z similar to 4. In order to derive the QLF based on our spectroscopic follow-up campaign, we estimated the photometric completeness of our quasar survey through detailed Monte Carlo simulations. Our QLF at z similar to 4 has a much shallower faint-end slope (beta = -1.67(-0.17)(+ 0.11)) than that obtained by other recent surveys in the same redshift. Our result is consistent with the scenario of downsizing evolution of active galactic nuclei inferred by recent optical and X-ray quasar surveys at lower redshifts.

DOI： 10.1088/2041-8205/728/2/L25

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We analyze the optical-near infrared spectra of 33 quasars with redshifts 3.9 &lt;= z &lt;= 6.4 to investigate the properties of dust extinction at these cosmic epochs. The SMC extinction curve has been shown to reproduce the dust reddening of most quasars at z &lt; 2.2; we investigate whether this curve also provides a good description of dust extinction at higher redshifts. We fit the observed spectra with synthetic absorbed quasar templates obtained by varying the intrinsic slope (alpha(lambda)), the absolute extinction (A(3000)), and by using a grid of empirical and theoretical extinction curves. We find that seven quasars in our sample are affected by substantial extinction (A(3000) &gt;= 0.8), and characterized by very steep intrinsic slopes (alpha(lambda) &lt;= -2.3). All of the individual quasars require extinction curve deviating from that of the SMC, with a tendency to flatten at lambda &lt;= 2000 angstrom (in the rest frame of the source). However, due to the uncertainties in the individual extinction curves the SMC is still (marginally) consistent with the data in most cases. We obtain a mean extinction curve at z &gt; 4, both by performing a simultaneous fit of all quasars and by averaging the extinction curves inferred for individual quasars. In the case of broad absorption line quasars (which are generally more absorbed by dust and possibly in a younger evolutionary stage), the mean extinction curve deviates from the SMC at a confidence level &gt;= 95%. The difference between extinction curves in quasars at z &gt; 4 and in quasars at lower redshift is indicative of either a different dust production mechanism at high redshift, or a different mechanism for processing dust into the ISM. We suggest that the same transitions may also apply to normal, star-forming galaxies at z &gt; 4. In particular, the observed change in the average spectral slope of galaxies at z &gt; 4 may be partially ascribed to a variation in the extinction curve, rather than a lower dust content at high redshift. In this scenario, the extinction curve inferred at z &gt; 4 would imply a cosmic star-formation corrected for dust attenuation a factor of similar to 2 higher than estimated in the past.

DOI： 10.1051/0004-6361/201014721

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present infrared, optical, and X-ray data of 48 X-ray bright, optically dull active galactic nuclei (AGNs) in the COSMOS field. These objects exhibit the X-ray luminosity of an AGN but lack broad and narrow emission lines in their optical spectrum. We show that despite the lack of optical emission lines, most of these optically dull AGNs are not well described by a typical passive red galaxy spectrum: instead they exhibit weak but significant blue emission like an unobscured AGN. Photometric observations over several years additionally show significant variability in the blue emission of four optically dull AGNs. The nature of the blue and infrared emission suggest that the optically inactive appearance of these AGNs cannot be caused by obscuration intrinsic to the AGNs. Instead, up to similar to 70% of optically dull AGNs are diluted by their hosts, with bright or simply edge-on hosts lying preferentially within the spectroscopic aperture. The remaining similar to 30% of optically dull AGNs have anomalously high f(X)/f(O) ratios and are intrinsically weak, not obscured, in the optical. These optically dull AGNs are best described as a weakly accreting AGN with a truncated accretion disk from a radiatively inefficient accretion flow.

DOI： 10.1088/0004-637X/706/1/797

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We present new deep optical spectra of 9 high-z radio galaxies (HzRGs) at z &gt; 2.7 obtained with FORS2 on VLT. These rest-frame ultraviolet spectra are used to infer the metallicity of the narrow-line regions (NLRs) in order to investigate the chemical evolution of galaxies in the high-z universe. We focus mainly on the Civ/He II and C III]/C IV flux ratios that are sensitive to both the gas metallicity and ionization parameter. Although the N V emission has been widely used to infer the gas metallicity, it is often too weak to be measured accurately for NLRs. In combining our new spectra with data from the literature, we examine the possible redshift evolution of the NLR metallicity for 57 HzRGs at 1 less than or similar to z less than or similar to 4. Based on the comparison between the observed emission-line flux ratios and the results of our photoionization model calculations, we find no significant metallicity evolution in NLRs of HzRGs, up to z similar to 4. Our results imply that massive galaxies had almost completed their chemical evolution at much higher redshift (z &gt; 5). Finally, although we detect strong N V emission lines in 5 HzRGs at z &gt; 2.7, we point out that high N V/He II ratios are not indicative of high metallicities but correspond to high ionization parameters of gas clouds in NLRs.

DOI： 10.1051/0004-6361/200811478

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0004-637X/700/2/971

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present detailed morphological properties of Ly alpha emitters ( LAEs) at z approximate to 5.7 in the COSMOS field based on Hubble Space Telescope Advanced Camera for Surveys ( ACS) data. The ACS imaging in the F814W filter covered 85 LAEs of the 119 LAEs identified in the full two square degree field, and 47 LAEs of them are detected in the ACS images. Nearly half of them are spatially extended with a size larger than 0.15 arcsec (similar to 0.88 kpc at z = 5.7) and up to 0.4 arcsec (similar to 2.5 kpc at z = 5.7). The others are nearly unresolved compact objects. Two LAEs show double-component structures indicating interaction or merging of building components to form more massive galaxies. By stacking the ACS images of all the detected sources, we obtain a Sersic parameter of n similar to 0.7 with a half-light radius of 0.13 arcsec ( 0.76 kpc), suggesting that the majority of ACS detected LAEs have not spheroidal-like but disk-like or irregular light profiles. Comparing ACS F814W magnitudes ( I(814)) with Subaru/Suprime-Cam magnitudes in the NB816, i&apos;, and z&apos; bands, we find that the ACS imaging in the F814W band mainly probes UV continuum rather than Ly alpha line emission. UV continuum sizes tend to be larger for LAEs with larger Ly alpha emission regions as traced by the NB816 imaging. The nondetection of 38 LAEs in the ACS images is likely due to the fact that their surface brightness is too low both in the UV continuum and Ly alpha emission. Estimating I(814) for the ACS-undetected LAEs from the z&apos; and NB816 magnitudes, we find that 16 of these are probably LAEs with a size larger than 0.15 arcsec in UV continuum. All these results suggest that our LAE sample contains systematically larger LAEs in UV continuum size than those previously studied at z similar to 6.

DOI： 10.1088/0004-637X/701/2/915

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present black hole masses and accretion rates for 182 Type 1 active galactic nuclei (AGNs) in COSMOS. We estimate masses using the scaling relations for the broad H beta, Mg II, and C IV emission lines in the redshift ranges 0.16 &lt; z &lt; 0.88, 1 &lt; z &lt; 2.4, and 2.7 &lt; z &lt; 4.9. We estimate the accretion rate using an Eddington ratio L(I)/L(Edd) estimated from optical and X-ray data. We find that very few Type 1 AGNs accrete below L(I)/L(Edd) similar to 0.01, despite simulations of synthetic spectra which show that the survey is sensitive to such Type 1 AGNs. At lower accretion rates the broad-line region may become obscured, diluted, or nonexistent. We find evidence that Type 1 AGNs at higher accretion rates have higher optical luminosities, as more of their emission comes from the cool (optical) accretion disk with respect to shorter wavelengths. We measure a larger range in accretion rate than previous works, suggesting that COSMOS is more efficient at finding low accretion rate Type 1 AGNs. However, the measured range in accretion rate is still comparable to the intrinsic scatter from the scaling relations, suggesting that Type 1 AGNs accrete at a narrow range of Eddington ratio, with L(I)/L(Edd) similar to 0.1.

DOI： 10.1088/0004-637X/700/1/49

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We report the detection of the [CII] 157.74 mu m fine-structure line in the lensed galaxy BRI 0952-0115 at z = 4.43, using the APEX telescope. This is the first detection of the [CII] line in a source with L(FIR) &lt; 10(13) L(circle dot) at high redshift. The line is much stronger than previous [CII] detections at high-z (a factor of 5-8 higher in flux), partly due to the lensing amplification. The L([CII])/ L(FIR) ratio is 10(-2.9), which is higher than observed in local galaxies with similar infrared luminosities. Together with previous observations of [CII] at high redshift, our result suggests that the [CII] emission in high-redshift galaxies is enhanced relative to local galaxies with the same infrared luminosity. This finding may result from selection effects of the few current observations of [CII] at high redshift and, in particular, from non detections that may not have been published ( although the few published upper limits are still consistent with the [CII] enhancement scenario). If the trend is confirmed with larger samples, it would indicate that high-z galaxies are characterized by different physical conditions than for their local counterparts. Regardless of the physical origin of the trend, this effect would increase the potential of the [CII]158 mu m line to search and characterize high-z sources.

DOI： 10.1051/0004-6361/200912265

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/61.3.487

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

The application of the virial theorem to the broad-line region (BLR) of active galactic nuclei (AGNs) allows black hole (BH) mass estimates for large samples of objects at all redshifts. In a recent paper, we showed that ionizing radiation pressure onto BLR clouds affects virial BH mass estimates and we provided empirically calibrated corrections. More recently, a new test of the importance of radiation forces has been proposed: the M(BH)-sigma relation has been used to estimate M(BH) for a sample of type-2 AGNs and virial relations (with and without radiation pressure) for a sample of type-1 AGNs extracted from the same parent population. The observed L/L(Edd) distribution based on virial BH masses is in good agreement with that based on M(BH)-sigma only if radiation pressure effects are negligible, otherwise significant discrepancies are observed. In this Letter, we investigate the effects of intrinsic dispersions associated with the virial relations providing M(BH), and we show that they explain the discrepancies between the observed L/L(Edd) distributions of type-1 and type-2 AGNs. These discrepancies in the L/L(Edd) distributions are present regardless of the general importance of radiation forces, which must be negligible only for a small fraction of sources with large L/L(Edd). Average radiation pressure corrections should then be applied in virial M(BH) estimators until their dependence on observed source physical properties has been fully calibrated. Finally, the comparison between M(BH) and L/L(Edd) distributions derived from sigma-based and virial estimators can constrain the variance of BLR physical properties in AGNs.

DOI： 10.1088/0004-637X/698/2/L103

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present results of a survey for Ly alpha emitters at z approximate to 4.86 based on optical narrowband (lambda(c) = 7126 angstrom, Delta lambda = 73 angstrom) and broadband (B, V, r&apos;, i&apos;, and z&apos;) observations of the Cosmic Evolution Survey field using Suprime-Cam on the Subaru Telescope. We find 79 Ly alpha emitter (LAE) candidates at z approximate to 4.86 over a contiguous survey area of 1.83 deg(2), down to the Ly alpha line flux of 1.47 x 10(-17) erg s(-1) cm(-2). We obtain the Ly alpha luminosity function with a best-fit Schechter parameters of log L* = 42.9(-0.3)(+0.5) erg s(-1) and phi* = 1.2(-1.1)(+8.0) x 10(-4) Mpc(-3) for alpha = -1.5 (fixed). The two-point correlation function for our LAE sample is xi(r) = (r/4.4(-2.9)(+5.7) Mpc)(-1.90 +/- 0.22). In order to investigate the field-to-field variations of the properties of Ly alpha emitters, we divide the survey area into nine tiles of 0 degrees.5 x 0 degrees.5 each. We find that the number density varies with a factor of similar or equal to 2 from field to field with high statistical significance. However, we find no significant field-to-field variance when we divide the field into four tiles with 0 degrees.7 x 0 degrees.7 each. We conclude that at least 0.5 deg(2) survey area is required to derive averaged properties of LAEs at z similar to 5, and our survey field is wide enough to overcome the cosmic variance.

DOI： 10.1088/0004-637X/696/1/546

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We investigate the optical emission-line flux ratios of narrow-line regions in order to determine whether the formation of active galactic nucleus (AGN) jets requires specific accretion conditions. We find that bright compact radio galaxies, which are powerful radio galaxies in the early stage of the jet activity, exhibit systematically larger flux ratios of [O I]lambda 6300/[O III]lambda 5007 and smaller flux ratios of [O III]lambda 5007/[O III]lambda 4363 than radio-quiet (RQ) Seyfert 2 galaxies. Comparing the observed line ratios with photoionization models, it is found that the difference in the flux ratio of low-to high-ionization lines (e. g., [O I]lambda 6300/[O III]lambda 5007) can be well understood by the difference in the spectral energy distribution (SED) of ionizing sources. Powerful young radio-loud (YRL) AGNs favor SED without a strong big blue bump (BBB), i.e., a radiatively inefficient accretion flow (RIAF), while RQ AGNs are consistent with the models adopting SED with a strong BBB, i. e., a geometrically thin, optically thick disk. These findings imply that the formation of powerful AGN jets requires the accretion disk with harder ionizing SED (i. e., an RIAF). We discuss the obscuring structure of YRL AGNs as a plausible origin of the difference in flux ratios of [O III]lambda 5007/[O III]lambda 4363.

DOI： 10.1088/0004-637X/693/2/1686

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We investigate the metallicity of the broad line region (BLR) of a sample of 30 quasars in the redshift range 4 &lt;z &lt; 6.4, by using near-IR and optical spectra. We focus on the ratio of the broad lines (SiIV1397+OIV] 1402)/CIV1549, which is a good metallicity tracer of the BLR. We find that the metallicity of the BLR is very high even in QSOs at z similar to 6. The inferred metallicity of the BLR gas is so high ( several times solar) that metal ejection or mixing with lower metallicity gas in the host galaxy is required to match the metallicities observed in local massive galaxies. On average, the observed metallicity changes neither among quasars in the observed redshift range 4 &lt; z &lt; 6.4, nor when compared with quasars at lower redshifts. We show that the apparent lack of metallicity evolution is a likely consequence of both the black hole-galaxy co-evolution and of selection effects. The data also suggest a lack of evolution in the carbon abundance, even among z &gt; 6 quasars. The latter result is puzzling, since the minimum enrichment timescale of carbon is about 1 Gyr, i.e. longer than the age of the universe at z similar to 6.

DOI： 10.1051/0004-6361:200811415

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

We present our analysis on the clustering properties of star-forming galaxies selected by narrow-band excesses in the Subaru Deep Field. Specifically, we focus on H alpha emitting galaxies at z = 0.24 and z = 0.40 in the same field, to investigate possible evolutionary signatures of clustering properties of star-forming galaxies. Based on an analysis on 228 H alpha emitting galaxies with 39.8 &lt; log L(H alpha) &lt; 40.8 at z = 0.40. we find that their two-point correlation function can be estimated as xi = (r/1.62(-0.50)(+0.64) Mpc)(-1.84+/-0.08). This is similar to that of H alpha emitting galaxies in the same H alpha luminosity range at z = 0.24, xi = (r/1.88(-0.49)(+0.60) Mpc)(-1.89+/-0.07). These correlation lengths are smaller than those for a brighter galaxy sample studied by Meneux er al. (2006) in the same redshift range. The evolution of the correlation length between z = 0.24 and z = 0.40 is interpreted by the gravitational growth of the dark-matter halos.

DOI： 10.1093/pasj/60.6.1249

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We present initial results of an ESO-VLT large programme (AMAZE) aimed at determining the evolution of the mass-metallicity relation at z &gt; 3 by means of deep near-IR spectroscopy. Gas metallicities are measured, for an initial sample of nine star forming galaxies at z similar to 3.5, by means of optical nebular lines redshifted into the near-IR. Stellar masses are accurately determined by using Spitzer-IRAC data, which sample the rest-frame near-IR stellar light in these distant galaxies. When compared with previous surveys, the mass-metallicity relation inferred at z similar to 3.5 shows an evolution much stronger than observed at lower redshifts. The evolution is prominent even in massive galaxies, indicating that z similar to 3 is an epoch of major action in terms of star formation and metal enrichment also for massive systems. There are also indications that the metallicity evolution of low mass galaxies is stronger relative to high mass systems, an effect which can be considered the chemical version of the galaxy downsizing. The mass-metallicity relation observed at z similar to 3.5 is difficult to reconcile with the predictions of some hierarchical evolutionary models. Such discrepancies suggest that at z &gt; 3 galaxies are assembled mostly with relatively un-evolved sub-units, i.e. small galaxies with low star formation efficiency. The bulk of the star formation and metallicity evolution probably occurs once small galaxies are already assembled into bigger systems.

DOI： 10.1051/0004-6361:200809678

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present a new photometric search for high-z galaxies hosting Population III (Pop III) stars based on deep intermediate-band imaging observations obtained in the Subaru Deep Field (SDF), using Suprime-Cam on the Subaru Telescope. By combining our new data with the existing broadband and narrowband data, we searched for galaxies that emit strongly in both Ly alpha and He II lambda 1640 (dual emitters) and are promising candidates for Pop III-hosting galaxies at 3: 93 less than or similar to z less than or similar to 4.01 and 4: 57 less than or similar to z less than or similar to 4.65. Although we found 10 dual emitters, most of them turn out to be [O II]-[O III] dual emitters or H beta-(H alpha+[ NII]) dual emitters at z &lt; 1, as inferred from their broadband colors and from the ratio of the equivalent widths. No convincing candidate Ly alpha-He II dual emitter of SFR(PopIII) greater than or similar to 2 M(circle dot) yr(-1) was found by our photometric search in 4.03 x 10(5) Mpc(3) in the SDF. This result disfavors low-feedback models for Pop III star clusters and implies an upper limit on the Pop III SFR density of SFRD(PopIII) &lt; 5 x 10(-6) M(circle dot) yr(-1) Mpc(-3). This new selection method to search for Pop III-hosting galaxies should be useful in future narrowband surveys to achieve the first observational detection of Pop III-hosting galaxies at high redshifts.

DOI： 10.1086/587888

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We consider the effect of radiation pressure from ionizing photons on black hole (BH) mass estimates based on the application of the virial theorem to broad emission lines in AGN spectra. BH masses based only on the virial product Delta V(2)R and neglecting the effect of radiation pressure can be severely underestimated, especially in objects close to the Eddington limit. We provide an empirical calibration of the correction for radiation pressure, and we show that it is consistent with a simple physical model in which BLR clouds are optically thick to ionizing radiation and have average column densities of N(H) similar to 10(23) cm(-2). This value is remarkably similar to what is required in standard BLR photoionization models to explain observed spectra. With the inclusion of radiation pressure, the discrepancy between virial BH masses based on single-epoch spectra and on reverberation mapping data drops from 0.4 to 0.2 dex rms. The use of single-epoch observations as surrogates of reverberation mapping campaigns can thus provide more accurate BH masses than previously thought. Finally, we show that narrow-line Seyfert 1 (NLS1) galaxies have apparently low BH masses because they are radiating close to their Eddington limit. After the radiation pressure correction, NLS1 galaxies have BH masses similar to other broad-line AGNs and follow the same M(BH)-sigma(e)/L(sph) relations as other active and normal galaxies. Radiation forces arising from ionizing photon momentum deposition constitute an important physical effect which must be taken into account when computing virial BH masses.

DOI： 10.1086/529360

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present our survey for optically faint variable objects using multiepoch ( 8-10 epochs over 2-4 years) i'- band imaging data obtained with Subaru Suprime-Cam over 0.918 deg(2) in the Subaru/XMM-Newton Deep Field (SXDF). We found 1040 optically variable objects by image subtraction for all the combinations of images at different epochs. This is the first statistical sample of variable objects at depths achieved with 8-10 m class telescopes or the Hubble Space Telescope. The detection limit for variable components is i'(vari) similar to 25.5 mag. These variable objects were classified into variable stars, supernovae ( SNe), and active galactic nuclei ( AGNs), based on the optical morphologies, magnitudes, colors, and optical-mid- infrared colors of the host objects, spatial offsets of variable components from the host objects, and light curves. Detection completeness was examined by simulating light curves for periodic and irregular variability. We detected optical variability for 36% +/- 2% ( 51% +/- 3% for a bright samplewith i' &lt; 24.4mag) of X- ray sources in the field. Number densities of variable objects as functions of time intervals Delta t and variable component magnitudes i'vari are obtained. Number densities of variable stars, SNe, and AGNs are 120, 489, and 579 objects deg(-2), respectively. Bimodal distributions of variable stars in the color-magnitude diagrams indicate that the variable star sample consists of bright ( V similar to 22 mag) blue variable stars of the halo population and faint ( V similar to 23.5 mag) red variable stars of the disk population. There are a few candidates of RR Lyrae providing a possible number density of similar to 10(-2) kpc(-3) at a distance of &gt; 150 kpc from the Galactic center.

DOI： 10.1086/527467

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present the properties of active galactic nuclei (AGN) selected by optical variability in the Subaru/XMM-Newton Deep Field (SXDF). Based on the locations of variable components and light curves, 211 optically variable AGNs were reliably selected. We made three AGN samples; X-ray-detected optically nonvariable AGNs (XAs), X-ray-detected optically variable AGNs (XVAs), and X-ray-undetected optically variable AGNs (VAs). In the VA sample, we found a bimodal distribution of the ratio between the variable component flux and the host flux. One of these two components in the distribution, a class of AGNs with a faint variable component i'(vari) similar to 25 mag in bright host galaxies i' similar to 21 mag, is not seen in the XVA sample. These AGNs are expected to have low Eddington ratios if we naively consider a correlation between bulge luminosity and black hole mass. These galaxies have photometric redshifts z(photo) similar to 0.5 and we infer that they are low-luminosity AGNs with radiatively inefficient accretion flows (RIAFs). The properties of the XVA and VA objects and the differences from those of the XA objects can be explained within the unified scheme for AGNs. Optical variability selection for AGNs is an independent method and could provide a complementary AGN sample which even deep X-ray surveys have not found.

DOI： 10.1086/528788

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

To derive a new H alpha luminosity function and to understand the clustering properties of star-forming galaxies at z approximate to 0.24, we have made a narrowband imaging survey for H alpha-emitting galaxies in the Hubble Space Telescope (HST) COSMOS 2 square degree field. We used the narrowband filter NB816 (lambda(c) = 8150 angstrom, Delta lambda = 120 angstrom) and sampled H alpha emitters with EW(obs)(H alpha + [N II]) &gt; 12 angstrom in a redshift range between z = 0.233 and 0.251 corresponding to a depth of 70 Mpc. We obtained 980 H alpha-emitting galaxies in a sky area of 5540 arcmin(2), corresponding to a survey volume of 3.1 x 10(4) Mpc(3). We derive a H alpha luminosity function with a best-fit Schechter function parameter set of alpha=-1.35(-0.13)(+0.11), log phi* = -2.65(-0.38)(+0.27), and L*(ergs s(-1)) = 41.94(-0.23)(+0.38). The H alpha luminosity density is 2.7(-0.6)(+0.7) x 10(39) ergs s(-1) Mpc(-3). After subtracting the AGN contribution ( 15%) to the H alpha luminosity density, the star formation rate density is evaluated as 1.8(-0.4)(+0.7) x 10(-2) M(circle dot) yr(-1) Mpc(-3). The angular two-point correlation function of H alpha-emitting galaxies of log L(H alpha) &gt; 39.8 is well fit by a power-law form of w(theta) = 0.013(-0.001)(+0.002)theta(-0.88 +/- 0.03) , corresponding to the correlation function of xi(r) = (r/1.9 Mpc)(-1.88). We also find that the H alpha emitters with higher H alpha luminosity are more strongly clustered than those with lower luminosity.

DOI： 10.1086/523703

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We have identified a large-scale structure at z similar or equal to 0.73 in the COSMOS field, coherently described by the distribution of galaxy photometric redshifts, an ACS weak- lensing convergence map, and the distribution of extended X- ray sources in a mosaic of XMM- Newton observations. The main peak seen in these maps corresponds to a rich cluster with T-X = 3.51(-0.46)(+0.60) keV and L-X =( 1.56 +/- 0.04)x10(44) ergs s(-1) ( 0.1-2.4 keV band). We estimate an X- ray mass within r(500) corresponding to M-500 similar or equal to 1.6x 10(14) M-circle dot and a total lensing mass ( extrapolated by fitting a NFW profile) M-NFW =(6 +/- 3)x 10(15) M-circle dot. We use an automated morphological classification of all galaxies brighter than I-AB = 24 over the structure area to measure the fraction of early-type objects as a function of local projected density Sigma(10), based on photometric redshifts derived from ground-based deep multiband photometry. We recover a robust morphology-density relation at this redshift, indicating, for comparable local densities, a smaller fraction of early-type galaxies than today. Interestingly, this difference is less strong at the highest densities and becomes more severe in intermediate environments. We also find, however, local "inversions'' of the observed global relation, possibly driven by the large-scale environment. In particular, we find direct correspondence of a large concentration of disk galaxies to ( the colder side of) a possible shock region detected in the X- ray temperature map and surface brightness distribution of the dominant cluster. We interpret this as potential evidence of shock-induced star formation in existing galaxy disks, during the ongoing merger between two subclusters.Our analysis reveals the value of combining various measures of the projected mass density to locate distant structures and their potential for elucidating the physical processes at work in the transformation of galaxy morphologies.

DOI： 10.1086/516588

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We have carried out a wide-field imaging survey for [O II] lambda 3727 emitting galaxies at z approximate to 1: 2 in the HST COSMOS 2 square degree field using the Suprime-Cam on the Subaru Telescope. The survey covers a sky area of 6700 arcmin(2) in the COSMOS field, and a redshift range between 1.17 and 1.20 ( Delta z 0: 03), corresponding to a survey volume of 5: 56; 105 Mpc(3). We obtain a sample of 3176 [O II] emitting galaxies with observed emission-line equivalent widths greater than 268. Since our survey tends to sample brighter [O II] emitting galaxies, we also analyze a sample of fainter [O II] emitting galaxies found in the Subaru Deep Field (SDF). We find an extinction-corrected [ O II] luminosity density of 10(- 0: 06)(40: 35+0: 08) ergs s (-1) Mpc (-3), corresponding to star formation rate density of 0: 32(- 0: 04)(+0: 06) M-circle dot yr(-1) Mpc(-3) in the COSMOS field at z approximate to 1: 2. This is the largest survey for [O II] emitters beyond z 1 currently available.

DOI： 10.1086/518037

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We present observations with the IRAM Plateau de Bure Interferometer of three QSOs at z &gt; 5 aimed at detecting molecular gas in their host galaxies as traced by CO transitions. CO (5-4) is detected in SDSS J033829.31+ 002156.3 at z = 5.0267, placing it amongst the most distant sources detected in CO. The CO emission is unresolved with a beam size of similar to 1 '', implying that the molecular gas is contained within a compact region, less than similar to 3 kpc in radius. We infer an upper limit on the dynamical mass of the CO emitting region of similar to 3 x 10(10) M-circle dot/sin(i)(2). The comparison with the Black Hole mass inferred from near-IR data suggests that the BH-to-bulge mass ratio in this galaxy is significantly higher than in local galaxies. From the CO luminosity we infer a mass reservoir of molecular gas as high as M(H-2) = 2.2 x 10(10) M-circle dot, implying that the molecular gas accounts for a significant fraction of the dynamical mass. When compared to the star formation rate derived from the far-IR luminosity, we infer a very short gas exhaustion timescale (similar to 10(7) years), comparable to the dynamical timescale. CO is not detected in the other two QSOs (SDSS J083643.85+ 005453.3 and SDSS J163033.90+ 401209.6) and upper limits are given for their molecular gas content. When combined with CO observations of other type 1 AGNs, spanning a wide redshift range (0 &lt; z &lt; 6.4), we find that the host galaxy CO luminosity (hence molecular gas content) and the AGN optical luminosity (hence BH accretion rate) are correlated, but the relation is not linear: L-CO' proportional to [lambda L-lambda (4400 angstrom)](0.72). Moreover, at high redshifts (and especially at z &gt; 5) the CO luminosity appears to saturate. We discuss the implications of these findings in terms of black hole-galaxy co-evolution.

DOI： 10.1051/0004-6361:20078136

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/519081

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：UNIV CHICAGO PRESS  

We present deep optical imaging observations of 2 square degree area, covered by the Cosmic Evolution Survey ( COSMOS), made by the prime-focus camera ( Supreme-Cam) on the 8.2 m Subaru Telescope. Observations were done in six broadband [B ( 4459.7 angstrom), g' ( 4723.1 angstrom), V ( 5483.8 angstrom), r' ( 6213.0 angstrom), i' (7640.8 angstrom), z' ( 8855.0 angstrom)] and one narrowband ( NB816) filters. A total of 10(6) galaxies were detected to i'similar to 26.5 mag. These data, combined with observations at u* and K- band are used to construct the photometric catalogs for the COSMOS, to measure their photometric redshifts, multiband spectral energy distributions, and stellar masses, and to identify high-redshift candidates. This catalog provides multi-wave band data for scientific analysis of the COSMOS survey.

DOI： 10.1086/516596

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/516563

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We report new follow-up spectroscopy of i'-dropout galaxies with an NB921-band depression found in the Subaru Deep Field. The NB921-depressed i'-dropout selection method is expected to select galaxies with large equivalent-width Ly alpha emission over a wide redshift range, 6.0 less than or similar to z less than or similar to 6.5. Two of four observed targets show a strong emission line with a clear asymmetric profile, identified as Lya emitters at z = 6.11 and 6.00. Their rest-frame equivalent widths are 153 angstrom and 114 angstrom, which are lower limits on the intrinsic equivalent widths. Through our spectroscopic observations ( including previous ones) of NB921-depressed i'-dropout galaxies, we identified 5 galaxies in total with a rest-frame equivalent width larger than 100 angstrom at 6.0 less than or similar to z less than or similar to 6.5 out of 8 photometric candidates, which suggests that the NB921-depressed i'-dropout selection method is possibly an efficient way to search for Lya emitters with a large Lya equivalent width, in a wider redshift range than with usual narrow-band excess techniques. By combining these findings with our previous observational results, we infer that the fraction of broad-band selected galaxies having a rest-frame equivalent width larger than 100 angstrom is significantly higher at z similar to 6 (the cosmic age of similar to 1 Gyr) than that at z similar to 3 (similar to 2 Gyr), being consistent with the idea that the typical stellar population of galaxies is significantly younger at z similar to 6 than that at z similar to 3. The NB921-depressed i'-dropout galaxies may be interesting candidates for hosts of massive, zero-metallicity Population III stars.

DOI： 10.1051/0004-6361:20066177

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：BLACKWELL PUBLISHING  

We use observations from the Giant Metrewave Radio Telescope (GMRT) to measure the atomic hydrogen gas content of star-forming galaxies at z = 0.24 (i.e. a look-back time of similar to 3 Gyr). The sample of galaxies studied were selected from H alpha-emitting field galaxies detected in a narrow-band imaging survey with the Subaru Telescope. The Anglo-Australian Telescope was used to obtain precise optical redshifts for these galaxies. We then co-added the H I 21-cm emission signal for all the galaxies within the GMRT spectral line data cube. From the co-added signal of 121 galaxies, we measure an average atomic hydrogen gas mass of (2.26 +/- 0.90) x 10(9) M-circle dot. We translate this H I signal into a cosmic density of neutral gas at z = 0.24 of Omega(gas) = (0.91 +/- 0.42) x 10(-3). This is the current highest redshift at which Omega(gas) has been constrained from 21-cm emission and our value is consistent with that estimated from damped Ly alpha systems around this redshift. We also find that the correlations between the H alpha luminosity and the radio continuum luminosity and between the star formation rate (SFR) and the H I gas content in star-forming galaxies at z = 0.24 are consistent with the correlations found at z = 0. These two results suggest that the star formation mechanisms in field galaxies similar to 3 Gyr ago were not substantially different from the present, even though the SFR is three times higher.

DOI： 10.1111/j.1365-2966.2007.11540.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

SDF line-emitting galaxies in four narrowband filters at low and intermediate redshifts are presented. Broadband colors, follow-up optical spectroscopy, and multiple NB filters are used to distinguish H alpha, [O II], and [O III] emitters at z = 0.07-1.47 to construct their LFs. These LFs are derived down to faint magnitudes, allowing for an accurate determination of the faint-end slope. With a large (N similar to 200-900) sample for each redshift interval, a Schechter profile is fitted to each LF. Prior to dust extinction corrections, the [O III] and [O II] LFs agree reasonably well with those of Hippelein et al. The z = 0.08 H alpha LF, which reaches 2 orders of magnitude fainter than Gallego et al., is steeper by 25%. This indicates that there are more low-luminosity star-forming galaxies for z &lt; 0.1. The faint-end slope alpha and phi(star) show a strong redshift evolution, while L-star shows little evolution. The evolution in alpha indicates that low-luminosity galaxies have a stronger evolution compared to brighter ones. Integrated SFR densities are derived via H alpha, [O III], and [O II] for 0.07 &lt; z &lt; 1.47. A steep increase in the SFR density, as a function of redshift, is seen for 0.4 &lt; z &lt; 0.9. For z &gt; 1, the SFR densities are similar. The latter is consistent with previous UV and [O II] measurements. Below z &lt; 0.4, the SFR densities are consistent with several H alpha, [O II], and UV measurements, but others are a factor of 2 higher. For example, the z = 0.066-0.092 LF agrees with Jones & Bland-Hawthorn, but at z = 0.24 and 0.40, their number densities are twice as high. This discrepancy can be explained by cosmic variance.

DOI： 10.1086/510828

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/516597

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/516595

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report on the discovery of a new potential galaxy threshing system in the COSMOS 2 square degree field using the prime-focus camera, Suprime-Cam, on the 8.2 m Subaru Telescope. This system consists of a giant elliptical galaxy with M v ≈ -21.6 and a tidally disrupted satellite galaxy with M v PS -17.7 at a photometric redshift of z ≈ 0.08. This redshift is consistent with the spectroscopic redshift of 0.079 for the giant elliptical galaxy obtained from the Sloan Digital Sky Survey (SDSS) archive. The luminosity masses of the two galaxies are 3.7 × 10 12 and 3.7 × 10 9 M ⊙, respectively. The distance between the two galaxies is greater than 100 kpc. The two tidal tails emanating from the satellite galaxy extend over 150 kpc. This system would be the second well-defined galaxy threshing system found so far. © 2007. The American Astronomical Society. All rights reserved.

DOI： 10.1086/516581

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1086/508621

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

Generally the gas metallicity in distant galaxies can only be inferred by using a few prominent emission lines. Various theoretical models have been used to predict the relationship between emission line fluxes and metallicity, suggesting that some line ratios can be used as diagnostics of the gas metallicity in galaxies. However, accurate empirical calibrations of these emission line flux ratios from real galaxy spectra spanning a wide metallicity range are still lacking. In this paper we provide such empirical calibrations by using the combination of two sets of spectroscopic data: one consisting of low-metallicity galaxies with a measurement of [OIII]lambda 4363 taken from the literature, including spectra from the Sloan Digital Sky Survey (SDSS), and the other one consisting of galaxies in the SDSS database whose gas metallicity has been determined from various strong emission lines in their spectra. This combined data set constitutes the largest sample of galaxies with information on the gas metallicity available so far and spanning the widest metallicity range. By using these data we obtain accurate empirical relations between gas metallicity and several emission line diagnostics, including the R-23 parameter, the [NII]lambda 6584/H alpha and [OIII]lambda 5007/[NII]lambda 6584 ratios. Our empirical diagrams show that the line ratio [OIII]lambda 5007/[OII]lambda 3727 is a useful tool to break the degeneracy in the R23 parameter when no information on the [NII]lambda 6584 line is available. The line ratio [NeIII]lambda 3869/[OII]lambda 3727 also results to be a useful metallicity indicator for high-z galaxies, especially when the R23 parameter or other diagnostics involving [OIII]lambda 5007 or [NII]lambda 6584 are not available. Additional, useful diagnostics newly proposed in this paper are the line ratios of (H alpha+[NII]lambda lambda 6548,6584)/[SII]lambda 6720, [OIII]lambda 5007/H beta, and [OII]lambda 3727/H beta. Finally, we compare these empirical relations with photoionization models. We find that the empirical R-23-metallicity sequence is strongly discrepant with respect to the trend expected by models with constant ionization parameter. Such a discrepancy is also found for other line ratios. These discrepancies provide evidence for a strong metallicity dependence of the average ionization parameter in galaxies. In particular, we find that the average ionization parameter in galaxies increases by similar to 0.7 dex as the metallicity decreases from 2 Z circle dot to 0.05 Z circle dot, with a small dispersion. This result should warn about the use of theoretical models with constant ionization parameter to infer metallicities from observed line ratios.

DOI： 10.1051/0004-6361:20065216

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

We report an extensive search for Lyα emitters (LAEs) at z = 6.5 in the Subaru Deep Field. Subsequent spectroscopy with Subaru and Keck identified eight more LAEs, giving a total of 17 spectroscopically confirmed LAEs at z = 6.5. Based on this spectroscopic sample of 17, complemented by a photometric sample of 58 LAEs, we have derived a more accurate Lyα luminosity function of LAEs at z = 6.5, which reveals an apparent deficit at the bright end of ∼0.75 mag fainter L*, compared with that observed at z = 5.7. The difference in the LAE luminosity functions between z = 5.7 and 6.5 is significant at the 3 σ level, which is reduced to 2 σ when cosmic variance is taken into account. This result may imply that the reionization of the universe has not been completed at z = 6.5. We found that the spatial distribution of LAEs at z = 6.5 was homogeneous over the field. We discuss the implications of these results for the reionization of the universe. © 2006. The American Astronomical Society. All rights reserved.

DOI： 10.1086/504966

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Recently, Zheng et al. (2006) found evidence for an overdensity of galaxies around a radio-loud quasar, SDSS J0836+0054, at z = 5.8 (a 5 arcmin(2) field). We examined our deep optical imaging data (B, V, r', i', z', and NB816) taken with the Suprime-Cam on the Subaru Telescope. The NB816 narrow-band filter (X, 815 nm and Delta lambda = 12 nm) is suitable to search for Ly alpha emitters at z approximate to 5.7. We found a new strong Ly alpha emitter at z approximate to 5.7 close to object 13, identified by Zheng et al. (2006). Further, the non-detection of nine objects selected by Zheng et al. (2006) in our B, V, and r' images provides corroborative evidence to indicate that they are high-z objects.

DOI： 10.1093/pasj/58.3.499

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記述言語：英語   掲載種別：研究論文（学術雑誌）