Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/aca403

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

We report the detection of an ionized gas outflow from an X-ray active galactic nucleus hosted in a massive quiescent galaxy in a protocluster at z = 3.09 (J221737.29+001823.4). It is a type-2 QSO with broad (W₈₀ > 1000 km s⁻¹) and strong ($\mathrm{log}({L}_{[\mathrm{OIII}]}$/erg s⁻¹) ≈ 43.4) [O iii]λλ 4959,5007 emission lines detected by slit spectroscopy in three-position angles using Multi-Object Infra-Red Camera and Spectrograph (MOIRCS) on the Subaru telescope and the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) on the Keck-I telescope. In the all slit directions, [O iii] emission is extended to ∼15 physical kpc and indicates a powerful outflow spreading over the host galaxy. The inferred ionized gas mass outflow rate is 22 ± 3 M_⊙ yr⁻¹. Although it is a radio source, according to the line diagnostics using Hβ, [O ii], and [O iii], photoionization by the central QSO is likely the dominant ionization mechanism rather than shocks caused by radio jets. On the other hand, the spectral energy distribution of the host galaxy is well characterized as a quiescent galaxy that has shut down star formation several hundred Myr ago. Our results suggest a scenario that QSOs are powered after the shutdown of the star formation and help complete the quenching of massive quiescent galaxies at high redshift.

DOI： 10.3847/1538-4357/ac7f2d

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ac7f2d/pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing Ltd  

We examine the redshift evolution of density environments around 2163 radio galaxies with the stellar masses of similar to 10(9)-10(12) M (circle dot) between redshifts of z = 0.3-1.4, based on the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) and Faint Images of the Radio Sky at Twenty cm. We use the k-nearest neighbor method to measure the local galaxy number density around our radio galaxy sample. We find that the overdensities of the radio galaxies are weakly but significantly anticorrelated with redshift. This is consistent with the known result that the relative abundance of less-massive radio galaxies increases with redshift, because less-massive radio galaxies reside in relatively low-density regions. Massive radio galaxies with stellar masses of M (*) > 10(11) M (circle dot) are found in high density environments compared with the control sample galaxies with radio nondetection and matched stellar mass. Less-massive radio galaxies with M (*) < 10(11) M (circle dot) reside in average density environments. The fraction of the radio galaxies associated with the neighbors within a typical major merger scale, <70 kpc, is higher than (comparable to) that of the control galaxies at M (*) > 10(11) M (circle dot) (M (*) < 10(11) M (circle dot)). We also find that the local densities around the radio galaxies are anticorrelated with the radio luminosities and black hole mass accretion rates at a fixed stellar mass. These findings suggest that massive radio galaxies have matured through galaxy mergers in the past, and have supermassive black holes whose mass accretion almost ceased at z > 1.4, while less-massive radio galaxies undergo active accretion just at this epoch, as they have avoided such merger events.

DOI： 10.3847/1538-4357/ac77ee

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/ac6257

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing Ltd  

We present the environmental properties around high-z radio galaxies (HzRGs) at z similar to 4, which have been poorly investigated because of their rarity. We use the largest samples of HzRGs and g-dropout galaxy overdense regions at z similar to 4, which were constructed from the Hyper Suprime-Cam Subaru Strategic Program, to characterize the HzRG environments statistically. We measure the g-dropout galaxy overdensities around 21 HzRGs whose rest-frame 1.4 GHz radio luminosities (L (1.4 GHz)) are 10(26-27) W Hz(-1). We find that the overdensities around the faint HzRGs with L (1.4 GHz) similar to 10(26.0-26.5) W Hz(-1) tend to be higher than those of the g-dropout galaxies. On the other hand, no significant difference of density environments is found between the luminous HzRGs with L (1.4 GHz) similar to 10(26.5-27.0) W Hz(-1) and the g-dropout galaxies. The HzRGs are found to occupy more massive halos than g-dropout galaxies through a cross-correlation between the HzRGs and g-dropout galaxies. This trend is more pronounced in the faint HzRGs. These results are consistent with a scenario where HzRGs get older and more massive as the radio luminosity decreases. The HzRGs are expected to trace the progenitors of Local Cluster halos from their calculated halo mass. In addition, we find that surrounding galaxies tend to distribute along the radio jet major axis of the HzRGs at angular distances of less than or similar to 500 physical kpc. Our findings imply the onset of the filamentary structures around the HzRGs at z similar to 4.

DOI： 10.3847/1538-4357/ac441c

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

DOI： 10.3847/1538-4357/ac1b26

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ac1b26/pdf

Language：English   Publishing type：Research paper (scientific journal)  

We report a massive quiescent galaxy at zspec= -3.0922+0.008-0.004 spectroscopically confirmed at a protocluster in the SSA22 field by detecting the Balmer and Ca II absorption features with the multi-object spectrometer for infrared exploration on the Keck I telescope. This is the most distant quiescent galaxy confirmed in a protocluster to date. We fit the optical to mid-infrared photometry and spectrum simultaneously with spectral energy distribution (SED) models of parametric and nonparametric star formation histories (SFHs). Both models fit the observed SED well and confirm that this object is a massive quiescent galaxy with a stellar mass of log (M∗/M⊙=11.26+0.03-0.04 and 11.54+0.03-0.00 and a star formation rate of SFR/M⊙ yr-1 < 0.3 and = -0.01+0.03-0.01 for parametric and nonparametric models, respectively. The SFH from the former modeling is described as an instantaneous starburst whereas that of the latter modeling is longer-lived, but both models agree with a sudden quenching of the star formation at ~0.6 Gyr ago. This massive quiescent galaxy is confirmed in an extremely dense group of galaxies predicted as a progenitor of a brightest cluster galaxy formed via multiple mergers in cosmological numerical simulations. We discover three new plausible [O III]λ5007 emitters at 3.0791 ≤ zspec ≤ 3.0833 serendipitously detected around the target. Two of them just between the target and its nearest massive galaxy are possible evidence of their interactions. They suggest the future great size and stellar mass evolution of this massive quiescent galaxy via mergers.

DOI： 10.3847/1538-4357/ac0cf8

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-3881/ab98fe

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Other Link： https://iopscience.iop.org/article/10.3847/1538-3881/ab98fe

Language：English   Publishing type：Research paper (scientific journal)  

<jats:title>Abstract</jats:title>
<jats:p>We present our ALMA Band 8 observations of a damped Ly$\alpha$ absorption (DLA) system at $z = 3.150$ observed in the spectrum of the quasar Q2233+131 at $z = 3.295$. The optical counterpart of this DLA has been identified and it shows a double-peaked Ly$\alpha$ emission line. Since one possible origin of DLAs at high redshift is an outflowing gas from star-forming galaxies, DLA 2233+131 provides a good laboratory to investigate the nature of high-z DLAs. Motivated by this, we have carried out ALMA band 8 observations to study the [C ii] line in this system. However, we do not detect any significant emission line in the observed pass bands. Instead, we have serendipitously found three submm continuum sources in the observed sky area. One appears to be the quasar Q2233+131 itself while the other two sources are newly identified submm galaxies (SMGs), called SMG1 and SMG2 in this paper. They are located at a separation of ${4{^{\prime \prime }_{. } }7}$ and ${8{^{\prime \prime }_{. } }1}$ from Q2233+131, respectively. Their 646 μm fluxes are $6.35\:$mJy and $6.43\:$mJy, respectively, being higher than that of Q2233+131, $3.62\:$mJy. Since these two SMGs are not detected in the optical images obtained with the Hubble Space Telescope and the Subaru Telescope, they have a very red spectral energy distribution. It is, therefore, suggested that they are high-redshift galaxies or very dusty galaxies at intermediate redshift, although we cannot rule out the possibility that they are optically very faint SMG analogs at low redshift. Follow-up observations will be necessary to explore the nature of this interesting region.</jats:p>

DOI： 10.1093/pasj/psaa004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We search for galaxies with a strong Balmer break (Balmer break galaxies; BBGs) at z 6 over a 0.41 deg2 effective area in the COSMOS field. Based on rich imaging data, including data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), three candidates are identified by their extremely red K [3.6] colors, as well as by nondetection in the X-ray, optical, far-infrared, and radio bands. The nondetection in the deep ALMA observations suggests that they are not dusty galaxies but BBGs at z 6, although contamination from active galactic nuclei at z 0 cannot be completely ruled out for the moment. Our spectral energy distribution analyses reveal that the BBG candidates at z 6 have stellar masses of x 101 M, dominated by old stellar populations with ages of > 700 Myr. Assuming that all three candidates are real BBGs at z 6, we estimate the stellar mass density to be 2.411 x 104 M. Mpc-3. This is consistent with an extrapolation from the lower-redshift measurements. The onset of star formation in the three BBG candidates is expected to be several hundred million yr before the observed epoch of z 6. We estimate the star formation rate density (SI-RD) contributed by progenitors of the BBGs to be 2.4-12 x 10-5 Mc, yr-1 Mpc3 at z > 14 (99.7% confidence range). Our result suggests a smooth evolution of the SFRD beyond z = 8.

DOI： 10.3847/1538-4357/ab6596

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/ab464f

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Language：English   Publishing type：Research paper (scientific journal)  

Cosmological simulations predict that the Universe contains a network of intergalactic gas filaments, within which galaxies form and evolve. However, the faintness of any emission from these filaments has limited tests of this prediction. We report the detection of rest-frame ultraviolet Lyman-α radiation from multiple filaments extending more than one megaparsec between galaxies within the SSA22 protocluster at a redshift of 3.1. Intense star formation and supermassive black-hole activity is occurring within the galaxies embedded in these structures, which are the likely sources of the elevated ionizing radiation powering the observed Lyman-α emission. Our observations map the gas in filamentary structures of the type thought to fuel the growth of galaxies and black holes in massive protoclusters....

DOI： 10.1126/science.aaw5949

arXiv

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We present a study of the gas kinematics of star-forming galaxies associated
with protocluster 4C 23.56 at $z=2.49$ using $0''.4$ resolution CO (4-3) data
taken with ALMA. Eleven H$\alpha$ emitters (HAEs) are detected in CO (4-3),
including six HAEs that were previously detected in CO (3-2) at a coarser
angular resolution. The detections in both CO lines are broadly consistent in
the line widths and the redshifts, confirming both detections. With an increase
in the number of spectroscopic redshifts, we confirm that the protocluster is
composed of two merging groups with a total halo mass of $\log{(M_{\rm
cl}/M_{\odot})} =13.4-13.6$, suggesting that the protocluster would evolve into
a Virgo-like cluster ($>10^{14} M_{\odot}$). We compare the CO line widths and
the CO luminosities with galaxies in other (proto)clusters ($n_{\rm gal}=91$)
and general fields ($n_{\rm gal}=80$) from other studies. The 4C23.56
protocluster galaxies have CO line widths and luminosities comparable to other
protocluster galaxies on average. On the other hand, the CO line widths are on
average broader by $\approx50\%$ compared to field galaxies, while the median
CO luminosities are similar. The broader line widths can be attributed to both
effects of unresolved gas-rich mergers and/or compact gas distribution, which
is supported by our limited but decent angular resolution observations and the
size estimate of three galaxies. Based on these results, we argue that gas-rich
mergers may play a role in the retention of the specific angular momentum to a
value similar to that of field populations during cluster assembly, though we
need to verify this with a larger number of samples.

DOI： 10.3847/1538-4357/ab3b5b

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4365/ab238d

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4365/ab238d

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/ab1754

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ab1754

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Cambridge University Press  

Optical properties of infrared-bright (IR-bright) dust-obscured galaxies (DOGs) are reported. DOGs are faint in optical but very bright in mid-IR, which are powered by active star formation (SF) or active galactic nucleus (AGN), or both. The DOGs is a candidate population that are evolving from a gas-rich merger to a quasar. By combining three catalogs of optical (Subaru Hyper Suprime-Cam), near-IR (VIKING), and mid-IR (ALLWISE), we have discovered 571 IR-bright DOGs. Using their spectral energy distributions, we classified the selected DOGs into the SF-dominated DOGs and the AGN-dominated DOGs. We found that the SF-dominated DOGs show a redder optical color than the AGN-dominated DOGs. Interestingly, some DOGs shows extremely blue color in optical (blue-excess DOGs: bluDOGs). A possible origin for this blue excess is either the leaked AGN light or stellar UV light from nuclear starbursts. The BluDOGs may be in the transition phase from obscured AGNs to unobscured AGNs.

DOI： 10.1017/S1743921319002400

Scopus

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/aadfe4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/aae1ac

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Other Link： http://stacks.iop.org/0004-637X/866/i=2/a=140?key=crossref.0ec0e513a9a68350c7a7b8af8d48eb8a

Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present the near-infrared high-resolution imaging of an extremely dense group of galaxies at the core of the protocluster at z = 3.09 in the SSA22 field by using the adaptive optics AO188 and the Infrared Camera and Spectrograph on board the Subaru Telescope. The wide morphological variety of them suggests their ongoing dramatic evolutions. One of the two quiescent galaxies (QGs), the most massive one in the group, is a compact elliptical with an effective radius r(e) = 1.37 +/- 0.75 kpc. It supports the two-phase formation scenario of giant ellipticals today that a massive compact elliptical is formed at once and evolves in size and stellar mass by a series of mergers. Since this object is a plausible progenitor of a brightest cluster galaxy of one of the most massive clusters today, it requires strong size (greater than or similar to 10) and stellar mass (similar to four times by z = 0) growths. Another QG hosts an active galactic nucleus and is fitted with a model composed from a nuclear component and Sersic model. It shows a spatially extended [O III] lambda 5007 emission line compared to the continuum emission, plausible evidence of outflows. Massive star-forming galaxies (SFGs) in the group are two to three times larger than the field SFGs at similar redshift. Although we obtained the K-band image deeper than the previous one, we found no new candidate members. This implies a physical deficiency of low-mass galaxies with stellar mass M-* less than or similar to 4 x 10(10) M-circle dot and/or poor detection completeness of them owing to their diffuse morphologies.

DOI： 10.1093/mnras/stx920

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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We investigate gas contents of star-forming galaxies associated with
protocluster 4C23.56 at z = 2.49 by using the redshifted CO(3-2) and 1.1 mm
dust continuum with the Atacama Large Millimeter/submillimeter Array. The
observations unveil seven CO detections out of 22 targeted H$\alpha$ emitters
(HAEs) and four out of 19 in 1.1 mm dust continuum. They have high stellar mass
($M_{\star}>4\times 10^{10}$ $M_{\odot}$) and exhibit a specific star-formation
rate typical of main-sequence star forming galaxies at $z\sim2.5$. Different
gas mass estimators from CO(3-2) and 1.1 mm yield consistent values for
simultaneous detections. The gas mass ($M_{\rm gas}$) and gas fraction ($f_{\rm
gas}$) are comparable to those of field galaxies, with $M_{\rm gas}=[0.3,
1.8]\times10^{11} \times (\alpha_{\rm CO}/(4.36\times A(Z)$)) M$_{\odot}$,
where $\alpha_{\rm CO}$ is the CO-to-H$_2$ conversion factor and $A(Z)$ the
additional correction factor for the metallicity dependence of $\alpha_{\rm
CO}$, and $\langle f_{\rm gas}\rangle = 0.53 \pm 0.07$ from CO(3-2). Our
measurements place a constraint on the cosmic gas density of high-$z$
protoclusters, indicating the protocluster is characterized by a gas density
higher than that of the general fields by an order of magnitude. We found $\rho
(H_2)\sim 5 \times 10^9 \,M_{\odot}\,{\rm Mpc^{-3 } }$ with the CO(3-2)
detections. The five ALMA CO detections occur in the region of highest galaxy
surface density, where the density positively correlates with global
star-forming efficiency (SFE) and stellar mass. Such correlations imply a
potentially critical role of environment on early galaxy evolution at high-z
protoclusters, although future observations are necessary for confirmation.

DOI： 10.3847/1538-4357/aa74c2

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We investigate the physical conditions of ionized gas in high-z star-forming galaxies using diagnostic diagrams based on the rest-frame optical emission lines. The sample consists of 701 galaxies with an H alpha detection at 1.4 less than or similar to z less than or similar to 1.7, from the Fiber Multi-Object Spectrograph (FMOS)-COSMOS survey, that represent the normal star-forming population over the stellar mass range 10(9.6) less than or similar to M-*/M-circle dot less than or similar to 10(11.6), with those at M-* &gt; 10(11)M(circle dot) being well sampled. We confirm an offset of the average location of star-forming galaxies in the Baldwin-PhillipsTerlevich (BPT) diagram ([O III] H beta versus [N II] H alpha), primarily toward higher [O III]/H beta, compared with local galaxies. Based on the [S II] ratio, we measure an electron density (n(e) = 220(-130)(+170) cm(-3)), which is higher than that of local galaxies. Based on comparisons to theoretical models, we argue that changes in emission-line ratios, including the offset in the BPT diagram, are caused by a higher ionization parameter both at fixed stellar mass and at fixed metallicity, with additional contributions from a higher gas density and possibly a hardening of the ionizing radiation field. Ionization due to active galactic nuclei is ruled out as assessed with Chandra. As a consequence, we revisit the mass-metallicity relation using [NII]/H alpha and a new calibration including [N II] [S II] as recently introduced by Dopita et al. Consistent with our previous results, the most massive galaxies (M-* greater than or similar to 10(11)M(circle dot)) are fully enriched, while those at lower masses have metallicities lower than local galaxies. Finally, we demonstrate that the stellar masses, metallicities, and star formation rates of the FMOS sample are well fit with a physically motivated model for the chemical evolution of star-forming galaxies.

DOI： 10.3847/1538-4357/835/1/88

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We study the extent to which very bright (-23.0 &lt; M-UV &lt; -21.75) Lyman-break-selected galaxies at redshifts z similar or equal to 7 display detectable Ly alpha emission. To explore this issue, we obtained follow-up optical spectroscopy of 9 z similar or equal to 7 galaxies from a parent sample of 24 z similar or equal to 7 galaxy candidates selected from the 1.65 deg(2) COSMOS-UltraVISTA and SXDS-UDS survey fields using the latest near-infrared public survey data, and new ultra-deep Subaru z'-band imaging (which we also present and describe in this paper). Our spectroscopy yielded only one possible detection of Ly alpha at z=7.168 with a rest-frame equivalent width EW0 = 3.7(-1.1)(+1.7) angstrom. The relative weakness of this line, combined with our failure to detect Ly alpha emission from the other spectroscopic targets, allows us to place a new upper limit on the prevalence of strong Ly alpha emission at these redshifts. For conservative calculation and to facilitate comparison with previous studies at lower redshifts, we derive a 1 sigma upper limit on the fraction of UV-bright galaxies at z similar or equal to 7 that display EW0 &gt; 50 angstrom, which we estimate to be &lt; 0.23. This result may indicate a weak trend where the fraction of strong Ly alpha emitters ceases to rise, and possibly falls between z similar or equal to 6 and z similar or equal to 7. Our results also leave open the possibility that strong Ly alpha may still be more prevalent in the brightest galaxies in the reionization era than their fainter counterparts. A larger spectroscopic sample of galaxies is required to derive a more reliable constraint on the neutral hydrogen fraction at z similar or equal to 7 based on the Ly alpha fraction in the bright galaxies.

DOI： 10.3847/0004-637X/822/1/46

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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

Web of Science

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Other Link： http://stacks.iop.org/0004-637X/819/i=1/a=25?key=crossref.dccb31bb4e762534b900334d6e3d6bfe

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We report the discovery of an extremely dense group of massive galaxies at the centre of the protocluster at z = 3.09 in the SSA22 field from near-infrared spectroscopy conducted with the multi-object infrared camera and spectrograph (MOIRCS) on the Subaru Telecope. The newly discovered group comprises seven galaxies confirmed at z(spec) approximate to 3.09 within 180 kpc, including fivemassive objectswith the stellarmasses larger than 10(10.5) M-circle dot and is associated with a bright submillimetre source SSA22-AzTEC14. The dynamical mass of the group estimated from the line-of-sight velocity dispersion of the members is M-dyn similar to 1.6 +/- 0.3 x 10(13)M(circle dot). Such a dense group is expected to be very rare at high redshift, as we have found only a few comparable systems in large-volume cosmological simulations. Such rare groups in simulations are hosted in collapsed haloes with M-vir = 10(13.4)-10(14.0)M(circle dot) and evolve into the brightest cluster galaxies (BCGs) of the most massive clusters at present. The observed AzTEC14 group at z = 3.09 is therefore very likely to be a proto-BCG in the multiple merger phase. The observed total stellar mass of the group is 5.8(-2.0)(+5.1) x 10(11)M(circle dot), which suggests that over half the stellar mass of its descendant had been formed by z = 3. Moreover, we have identified over two members for each of the four Ly alpha blobs (LABs) using our new spectroscopic data. This verifies our previous argument that many of the LABs in the SSA22 protocluster associated with multiple developed stellar components.

DOI： 10.1093/mnras/stv2392

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

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 Hα emission line that falls within the H-band (1.6-1.8 μm) spectroscopic window from star-forming galaxies with 1.4 &lt
z &lt
1.7 and Mstellar 1010 Mo. 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 ∼ 2600) effectively separates Hα and [N ii]λ6585, 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 Hα detections are followed up with FMOS observations at shorter wavelengths using the J-long (1.11-1.35 μm) grating to detect Hβ and [O iii]λ5008 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

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

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 lowluminosity quasars at -24 &lt
M1450 &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 zLBG 25.0 &lt
at z ∼ 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 ∼ 4 is derived by utilizing the quasar-LBG CCF and the LBG autocorrelation 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 (MDM/(h-1Mo.)= 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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

We report a discovery of six massive galaxies with both extremely large Lyα equivalent widths (EWs) and evolved stellar populations at z ∼ 3. These MAssive Extremely STrong Lyα emitting Objects (MAESTLOs) have been discovered in our large-volume systematic survey for strong Lyα 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 EW&lt
inf&gt
0&lt
/inf&gt
(Lyα) ∼ 100-300, (2) M&lt
inf&gt
∗&lt
/inf&gt
∼ 10&lt
sup&gt
10.5&lt
/sup&gt
-10&lt
sup&gt
11.1&lt
/sup&gt
M&lt
inf&gt
o&lt
/inf&gt
, and (3) relatively low specific star formation rates of SFR/M&lt
inf&gt
∗&lt
/inf&gt
∼ 0.03-1 Gyr&lt
sup&gt
-1&lt
/sup&gt
. Three of the six MAESTLOs have extended Lyα 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 Lyα 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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP SCIENCES S A  

The relation between the stellar mass (M-star) and the star formation rate (SFR) characterizes how the instantaneous star formation is determined by the galaxy past star formation history and by the growth of the dark matter structures. We deconstruct the M-star-SFR plane by measuring the specific SFR functions in several stellar mass bins from z = 0.2 out to z = 1.4 (specific SFR = SFR/M-star, noted sSFR). Our analysis is primary based on a 24 mu m selected catalogue combining the COSMOS and GOODS surveys. We estimate the SFR by combining mid-and far-infrared data for 20500 galaxies. The sSFR functions are derived in four stellar mass bins within the range 9.5 &lt; log(M-star/M-circle dot) &lt; 11.5. First, we demonstrate the importance of taking into account selection effects when studying the M-star-SFR relation. Secondly, we find a mass-dependent evolution of the median sSFR with redshift varying as sSFR proportional to (1 + z)(b), with b increasing from b = 2.88(+/- 0.12) to b = 3.78(+/- 0.60) between M-star = 10(9.75) M-circle dot and M-star = 10(11.1) M-circle dot, respectively. At low masses, this evolution is consistent with the cosmological accretion rate and predictions from semi-analytical models (SAM). This agreement breaks down for more massive galaxies showing the need for a more comprehensive description of the star formation history in massive galaxies. Third, we obtain that the shape of the sSFR function is invariant with time at z &lt; 1.4 but depends on the mass. We observe a broadening of the sSFR function ranging from 0.28 dex at M-star = 10(9.75) M-circle dot to 0.46 dex at M-star = 10(11.1) M-circle dot. Such increase in the intrinsic scatter of the M-star-SFR relation suggests an increasing diversity of star formation histories (SFHs) as the stellar mass increases. Finally, we find a gradual decline of the sSFR with stellar mass as log(10)(sSFR) proportional to-0.17M(star). We discuss the numerous physical processes, as gas exhaustion in hot gas halos or secular evolution, which can gradually reduce the sSFR and increase the SFH diversity.

DOI： 10.1051/0004-6361/201425176

Web of Science

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Using the Hubble Space Telescope (HST)/WFC3 and Advanced Camera for Surveys multi-band imaging data taken in CANDELS and 3D-HST, we study the general properties and diversity of the progenitors of the Milky Way (MWs) and local massive galaxy (MGs) at 0.5 &lt; z &lt; 3.0, based on a constant cumulative number density analysis. After careful data reduction and stacking analysis, we conduct a radially resolved pixel spectral energy distribution fitting to obtain the radial distributions of the stellar mass and rest-frame colors. The stellar mass of MWs increases in a self-similar way, irrespective of the radial distance, while that of MGs grows in an inside-out way where they obtain similar to 75% of the total mass at the outer (&gt;2.5 kpc) radius since z similar to 2. Although the radial mass profiles evolve in distinct ways, the formation and quenching of the central dense region (or bulge) ahead of the formation of the outer disk are found to be common for both systems. The sudden reddening of the bulge at z similar to 1.6 and z similar to 2.4 for MWs and MGs, respectively, suggests the formation of the bulge and would give a clue to the different gas accretion histories and quenching. A new approach to evaluate the morphological diversity is conducted by using the average surface density profile and its dispersion. The variety of the radial mass profiles for MGs peaks at higher redshift (z &gt; 2.8) and then rapidly converges to a more uniform shape at z &lt; 1.5, while that for MWs remains in the outer region over the redshift. Compared with the observed star-formation rates and color profiles, the evolution of variety is consistently explained by the star-formation activities.

DOI： 10.1088/0004-637X/805/1/34

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

Using the Hubble Space Telescope/Wide Field Camera 3 imaging data and multi-wavelength photometric catalog, we investigated the dust temperature of passively evolving and star-forming galaxies at in the CANDELS fields. We estimated the stellar radiation field by low-mass stars from the stellar mass and surface brightness profile of these galaxies and then calculated their steady-state dust temperature. At first, we tested our method using nearby early-type galaxies with the deep far-IR data by the Herschel Virgo cluster survey and confirmed that the estimated dust temperatures are consistent with the observed temperatures within the uncertainty. We then applied the method to galaxies at 0.2 &lt
z &lt
1.0, and found that mostpassively evolving galaxies with Mstar &gt
1010 M⊙ have relatively high dust temperatures of Tdust &gt
20 K, for which the formation efficiency of molecular hydrogen on the surface of dust grains in the diffuse ISM is expected to be very low from the laboratory experiments. The fraction of passively evolving galaxies strongly depends on the expected dust temperature at all redshifts and increases rapidlyincreasing temperature around Tdust ∼ 20 K. These results suggest that the dust heating by low-mass stars in massive galaxies plays an important role in the continuation of their passive evolutionbecause the lack of the shielding effect of the molecular hydrogen on the UV radiation can prevent the gas cooling and formation of new stars.

DOI： 10.1088/0004-637X/801/2/134

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arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We compared the number of faint stars detected in deep survey fields with the current stellar distribution model of the Galaxy and found that the detected number in the H band is significantly smaller than the predicted number. This indicates that M-dwarfs, the major component, are fewer in the halo and the thick disk. We used archived data of several surveys in both the north and south field of GOODS (Great Observatories Origins Deep Survey), MODS (MOIRCS Deep Survey) in GOODS-N, and ERS (Early Release Science) and CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) in GOODS-S. The number density of M-dwarfs in the halo has to be 20%+/- 13% relative to that in the solar vicinity, in order for the detected number of stars fainter than 20.5 mag in the H band to match with the predicted value from the model. In the thick disk, the number density of M-dwarfs must be reduced (52%+/- 13%) or the scale height must be decreased (similar to 600 pc). Alternatively, overall fractions of the halo and thick disks can be significantly reduced to achieve the same effect, because our sample mainly consists of faint M-dwarfs. Our results imply that the M-dwarf population in regions distant from the Galactic plane is significantly smaller than previously thought. We then discussed the implications this has on the suitability of the model predictions for the prediction of non-companion faint stars in direct imaging extrasolar planet surveys by using the best-fitting number densities.

DOI： 10.1093/pasj/psu125

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University 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-b and (B, g′, V, r′, i′, and z′), two narrow-b and (NB711 and NB816), and 12 intermediate-b and 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-b and and one narrow-b and (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 b and s. We also present the optical properties of the Suprime-Cam IA filter system in appendices.

DOI： 10.1093/pasj/psv106

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arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.1088/0004-637x/799/1/38

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

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 1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The mass-metallicity (MZ) relation at z 1.6 is steeper than the relation observed in the local universe. The steeper MZ relation at z 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 1.6. The most massive galaxies at z 1.6 (1011 M) are enriched to the level observed in massive galaxies in the local universe. The MZ relation we measure at z 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 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. © 2014. The American Astronomical Society. All rights reserved..

DOI： 10.1088/0004-637X/792/1/75

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

Using the Hubble Space Telescope/Advanced Camera for Surveys data in the COSMOS field, we systematically searched clumpy galaxies at 0.2 &lt
z &lt
1.0 and investigated the fraction of clumpy galaxies and its evolution as a function of stellar mass, star formation rate (SFR), and specific SFR (SSFR). The fraction of clumpy galaxies in star-forming galaxies with Mstar &gt
109.5 M· decreases with time from ∼0.35 at 0.8 &lt
z &lt
1.0 to ∼0.05 at 0.2 &lt
z &lt
0.4, irrespective of the stellar mass, although the fraction tends to be slightly lower for massive galaxies with M star &gt
1010.5 M· at each redshift. On the other hand, the fraction of clumpy galaxies increases with increasing both SFR and SSFR in all the redshift ranges we investigated. In particular, we found that the SSFR dependences of the fractions are similar among galaxies with different stellar masses, and the fraction at a given SSFR does not depend on the stellar mass in each redshift bin. The evolution of the fraction of clumpy galaxies from z ∼ 0.9 to z ∼ 0.3 seems to be explained by such SSFR dependence of the fraction and the evolution of SSFRs of star-forming galaxies. The fraction at a given SSFR also appears to decrease with time, but this can be due to the effect of the morphological k correction. We suggest that these results are understood by the gravitational fragmentation model for the formation of giant clumps in disk galaxies, where the gas mass fraction is a crucial parameter. © 2014. The American Astronomical Society. All rights reserved.

DOI： 10.1088/0004-637X/786/1/15

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arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

We analyze the recently released Hubble Space Telescope/Wide Field Camera 3 IR images in the GOODS-N region to study the formation and evolution of quiescent galaxies (QGs). After examining the reliability of two-dimensional light profiles with artificial galaxies, we obtain the morphological parameters with Sérsic profile of 299 QGs and 1083 star-forming galaxies (SFGs) at z0.5-3.0, finding the evolution of r e and n of massive (M * ≥ 10 10.5 M ) QGs and weaker evolution of SFGs and less massive (M * &lt
1010.5 M ) QGs. The regression of the size evolution of massive QGs follows with (a factor of 2.2 increases from z2.5 to 0.5), which is consistent with the general picture of the significant size growth. For the further understanding of the evolution scenario, we study the evolution of the Sérsic index, n, and find that massive QGs significantly evolve as with α n = 0.74 ± 0.23 (n 1 at z2.5 to n 4 at z0.5), while those of the other populations are unchanged (n1) over the redshift range. The results in the present study are consistent with both observations and numerical simulations where a gas-poor minor merger is believed to be the main evolution scenario. By taking the connection with less massive QGs and SFGs into account, we discuss the formation and evolution of the massive QGs over "Cosmic High Noon" or the peak of star-formation in the universe. © 2014. The American Astronomical Society. All rights reserved..

DOI： 10.1088/0004-637X/785/1/18

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.1088/0004-637x/784/2/90

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

We study the properties of K-band-selected galaxies (K AB &lt
24) in the z = 3.09 SSA22 protocluster field. 430 galaxies at 2.6 &lt
z phot &lt
3.6 are selected as potential protocluster members in a 112 arcmin2 area based on their photometric redshifts. We find that ≈20% of the massive galaxies with stellar masses &gt
1011 M ⊙ at z phot ∼ 3.1 have colors consistent with those of quiescent galaxies with ages &gt
0.5 Gyr. This fraction increases to ≈50% after correcting for unrelated foreground/background objects. We also find that 30% of the massive galaxies are heavily reddened, dusty, star-forming galaxies. Few such quiescent galaxies at similar redshifts are seen in typical survey fields. An excess surface density of 24 μm sources at z phot ∼ 3.1 is also observed, implying the presence of dusty star-formation activity in the protocluster. Cross-correlation with the X-ray data indicates that the fraction of K-band-selected protocluster galaxies hosting active galactic nuclei (AGNs) is also high compared with the field. The sky distribution of the quiescent galaxies, the 24 μm sources, and the X-ray AGNs show clustering around a density peak of z = 3.1 Lyα emitters. A significant fraction of the massive galaxies have already become quiescent, while dusty star-formation is still active in the SSA22 protocluster. These findings indicate that we are witnessing the formation epoch of massive early-type galaxies in the centers of the predecessors to present-day rich galaxy clusters. © 2013. The American Astronomical Society. All rights reserved.

DOI： 10.1088/0004-637X/778/2/170

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Language：English   Publishing type：Research paper (scientific journal)  

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

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

We investigated the fraction of [O II] emitters in galaxies at z ∼ 0.9 as a function of the local galaxy density in the Hubble Space Telescope (HST) COSMOS 2 deg2 field. [O II] 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 [O II] emitters, to directly compare the results with our previous study at z ∼ 1.2. We found that the fraction is almost constant at 0.3 Mpc-2 &lt
Σ10th &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 ∼ 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 [O II] emitters decreases from ∼60% at z ∼ 1.2 to ∼30% at z ∼ 0.9 independent of galaxy environment. The decrease of the [O II] emitter fraction could be explained mainly by the rapid decrease of star formation activity in the universe from z ∼ 1.2 to z ∼ 0.9. © 2013. The American Astronomical Society. All rights reserved.

DOI： 10.1088/0004-637X/768/1/51

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.1088/0067-0049/206/1/3

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Other Link： https://iopscience.iop.org/article/10.1088/0067-0049/206/1/3

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

During the course of our Lyman continuum imaging survey, we found that the spectroscopically confirmed Lyα emitter LAE 221724+001716 at z = 3.10 in the SSA 22 field shows strong Lyman continuum emission (λrest ∼ 900 Å) that escapes from this galaxy. However, another recent spectroscopic survey revealed that the supposed Lyman continuum emission could arise from a foreground galaxy at z = 1.76 if the emission line newly detected from the galaxy at λobs ≈ 3360 Å is Lyα. If this is the case, as the angular separation between these two galaxies is very small (≈0.″6), LAE 221724+001716 at z = 3.10 could be amplified by the gravitational lensing caused by this intervening galaxy. Here we present a possible gravitational lens model for the system of LAE 221724+001716. First, we estimate the stellar mass of the intervening galaxy as M ⊙* ∼ 3.5 × 109 M⊙ from its UV luminosity and ∼3.0 × 107-2.4 × 10 9 M⊙ through the spectral energy distribution fitting. Then, we find that the gravitational magnification factor ranges from 1.01 to 1.16 using the so-called singular isothermal sphere model for strong lensing. While LAE 221724+001716 is the first system of an LAE-LAE lensing reported so far, the estimated magnification factor is not so significant because the stellar mass of the intervening galaxy is small. © 2013. The American Astronomical Society. All rights reserved.

DOI： 10.1088/0004-637X/766/2/122

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arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

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, Hα, [N II]λ6583/Hα, and [S II]λλ6716,6731/Hα maps were obtained with subarcsecond resolution. The superior spatial resolution compared to earlier studies reveals a number of bright Hα emitting clouds within the cap. The emission line widths (≲ 100 km s-1 FWHM) and line ratios in the newly identified knots are most reasonably explained by slow to moderate shocks velocities (vshock = 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 (fesc &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. © 2012. The American Astronomical Society. All rights reserved.

DOI： 10.1088/0004-637X/761/1/55

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

We present the result of our low-luminosity quasar survey in the redshift range of 4.5 ≲ z ≲ 5.5 in the COSMOS field. Using the COSMOS photometric catalog, we selected 15 quasar candidates with 22 &lt
i′ &lt
24 at z ∼ 5 that are ∼ 3mag 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 ∼ 5, while a low-luminosity type-2 quasar at z ∼ 5.07 was discovered. In order to constrain the faint end of the quasar luminosity function at z ∼ 5, we calculated the 1σ confidence upper limits of the space density of type-1 quasars. As a result, the 1σ confidence upper limits on the quasar space density are Φ &lt
1.33 × 10-7Mpc-3mag-1 for -24.52 &lt
M 1450 &lt
-23.52 and Φ &lt
2.88 × 10-7Mpc -3mag-1 for -23.52 &lt
M 1450 &lt
-22.52. The inferred 1σ 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 ∼ 5. We find that the quasar space density decreases gradually as a function of redshift at low luminosity (M 1450 ∼ -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. © 2012. The American Astronomical Society. All rights reserved.

DOI： 10.1088/0004-637X/756/2/160

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

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 Hα imaging has newly revealed large-scale Hα 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 Hα absorption region in the eastern bubble is 5kpc × 7.5kpc, and the observed Hα equivalent widths are 2 Å ± 0.2 Å. The sizes of the northern and southern Hα-absorption tidal tails are 5kpc × 10kpc and 6kpc × 20kpc, respectively. The observed Hα equivalent widths range from 4 Å to 7 Å. 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 1Gyr in Arp 220. © 2012 The American Astronomical Society. All rights reserved.

DOI： 10.1088/0004-637X/753/1/78

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present the results of wide-field deep JHK imaging of the SSA22 field using the MOIRCS instrument equipped with the Subaru telescope. The observed field is 112 arcmin(2) in area, which covers the z = 3.1 protocluster characterized by the overdensities of Ly alpha emitters (LAEs) and Ly alpha blobs (LABs). The 5 sigma limiting magnitude is K-AB = 24.3. We extract the potential protocluster members from the K-selected sample by using the multi-band photometric-redshift selection as well as the simple color cut for distant red galaxies (DRGs; J - K-AB &gt; 1.4). The surface number density of DRGs in our observed fields shows clear excess compared with those in the blank fields, and the location of the densest area whose projected overdensity is twice the average coincides with the large-scale density peak of LAEs. We also found that K-band counterparts with z(phot) similar or equal to 3.1 are detected for 75% (15/20) of the LABs within their Ly alpha halo, and the 40% (8/20) of LABs have multiple components, which gives a direct evidence of the hierarchical multiple merging in galaxy formation. The stellar mass of LABs correlates with their luminosity, isophotal area, and the Ly alpha velocity widths, implying that the physical scale and the dynamical motion of Ly alpha emission are closely related to their previous star formation activities. Highly dust-obscured galaxies such as hyper extremely red objects (J - K-AB &gt; 2.1) and plausible K-band counterparts of submillimeter sources are also populated in the high-density region.

DOI： 10.1088/0004-637X/750/2/116

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

We present scaling relations between the stellarmass (M-*) and size of galaxies at 0.3 &lt; z &lt; 3 for half-light (R-50) and 90 per cent-light (R-90) radii, using a deep K-band-selected catalogue taken with the Subaru Telescope and Multi-Object Infrared Camera and Spectrograph (MOIRCS) in the Great Observatories Origins Deep Survey (GOODS)-North region. The logarithmic slope R proportional to M-*(0.1-0.2) is independent of redshift in a wide mass range of M-* similar to 10(8)-10(11) M-circle dot, irrespective of galaxy populations (star forming and quiescent). The offset change is less than or similar to 50 per cent. Provided that optical light in the rest frame traces the stellar mass of galaxies, the universal relation demonstrates that the stellar mass was built up in galaxies over their cosmic histories in a similar manner on average, irrespective of galaxy mass. The small offset in each stellar mass bin from the universal relation shows weak size evolution at a given mass. There is a moderate increase of 30-50 per cent for R-50 and R-90 for less massive galaxies (M-* &lt; 10(10) M-circle dot) from z similar to 3 to 1, while the sizes remain unchanged or slightly decreased towards z similar to 0.3. For massive galaxies (M-* similar to 10(11) M-circle dot), the evolution increases by similar to 70-80 per cent in R-90 from z similar to 3 to 0.3, though it is weaker in R-50. The evolution of compactness factor, R-50/R-90, which becomes smaller at lower redshift, is suggestive of minor merging effect in the outer envelope of massive galaxies.

DOI： 10.1111/j.1365-2966.2012.20674.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

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 ≃ 1.2 galaxies in the 2deg2 COSMOS field. We estimate star formation using the [O II]λ3727 emission line and environment from the local galaxy density. Our analysis shows that for massive galaxies (M * ≳ 10 10 M ⊙), the fraction of [O II] emitters in high-density environments (Σ10th ≳ 3.9 Mpc-2) is 1.7 0.4 times higher than in low-density environments (Σ10th ≲ 1.5 Mpc-2), while the [O II] emitter fraction does not depend on environment for low-mass M * ≲ 1010 M ⊙ 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 * ≳ 1010 M ⊙. 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 ∼ 1.2, increasing the fraction of star-forming galaxies with M * ≳ 1010 M ⊙. © 2012. The American Astronomical Society. All rights reserved.

DOI： 10.1088/0004-637X/747/1/42

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

We study the structure of star-forming galaxies at z ∼ 2 in a Great Observatories Origins Deep Survey North field selected as star-forming BzK (sBzK) galaxies down to KAB &lt
24.0 mag. Among 1029 sBzK galaxies, 551 galaxies (54%) show a single component in the Advanced Camera for Survey (ACS)/F850LP image obtained with the Hubble Space Telescope
the rest show multiple components. We fit the single-component sBzK galaxies with the single Sérsic profile using the ACS/F850LP image and find that a majority of them (64%) show a Sérsic index of n = 0.5-2.5, indicating that they have a disk-like structure. The resulting effective radii typically range from 1.0 to 3.0 kpc in the rest-frame UV wavelength. After correcting the effective radii to those in the rest-frame optical wavelength, we find that the single-component sBzK galaxies are located in the region where the local and z 1 disk galaxies are distributed in the stellar-mass-size diagram, suggesting comparable surface stellar-mass density between the sBzK and z 0-1 disk galaxies. All these properties suggest that the single-component sBzK galaxies are progenitors of the present-day disk galaxies. However, by studying their intrinsic shape through comparison between the observed distribution of apparent axial ratios and the distribution for triaxial models with axes A &gt
B &gt
C, we find that the mean B/A ratio is 0.61+0.05-0.08 and disk thickness C/A is 0.28+0.03-0.04. This indicates that the single-component sBzK galaxies at z ∼ 2 have a bar-like or oval shape rather than a round disk shape. The shape seems to resemble a bar/oval structure that forms through bar instability
if this is the case, the intrinsic shape may give us a clue to understand dynamical evolution of baryonic matter in a dark matter halo. © 2011. The American Astronomical Society. All rights reserved.

DOI： 10.1088/0004-637X/736/2/92

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Based on the ultraviolet to far-infrared photometry already compiled and presented in a companion paper (Paper I), we present a detailed spectral energy distribution (SED) analysis of nearly 80,000 IRAC 3.6 + 4.5 mu m selected galaxies in the Extended Groth Strip. We estimate photometric redshifts, stellar masses, and star formation rates (SFRs) separately for each galaxy in this large sample. The catalog includes 76,936 sources with [3.6] &lt;= 23.75 (85% completeness level of the IRAC survey) over 0.48 deg(2). The typical photometric redshift accuracy is Delta z/(1 + z) = 0.034, with a catastrophic outlier fraction of just 2%. We quantify the systematics introduced by the use of different stellar population synthesis libraries and initial mass functions in the calculation of stellar masses. We find systematic offsets ranging from 0.1 to 0.4 dex, with a typical scatter of 0.3 dex. We also provide UV- and IR-based SFRs for all sample galaxies, based on several sets of dust emission templates and SFR indicators. We evaluate the systematic differences and goodness of the different SFR estimations using the deep FIDEL 70 mu m data available in the Extended Groth Strip. Typical random uncertainties of the IR-bases SFRs are a factor of two, with non-negligible systematic effects at z greater than or similar to 1.5 observed when only MIPS 24 mu m data are available. All data products (SEDs, postage stamps from imaging data, and different estimations of the photometric redshifts, stellar masses, and SFRs of each galaxy) described in this and the companion paper are publicly available, and they can be accessed through our the Web interface utility Rainbow-navigator.

DOI： 10.1088/0067-0049/193/2/30

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/63.sp2.s379

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Language：English  

DOI： 10.1093/pasj/63.sp2.S415

CiNii Books

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/63.sp2.s403

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We investigated rest-frame near-infrared (NIR) morphologies of a sample of 139 galaxies with M-s &gt;= 1 x 10(10) M-circle dot at z = 0.8-1.2 in the GOODS-North field using our deep NIR imaging data (MOIRCS Deep Survey, MODS). We focused on Luminous Infrared Galaxies (LIRGs), which dominate a high star formation rate (SFR) density at z similar to 1, in a sample identified by cross-correlating with the Spitzer/MIPS 24 mu m source catalog. We performed two-dimensional light profile fittings of z similar to 1 galaxies in the K-s-band (rest-frame J-band) with a single-component Sersic model. We found that at z similar to 1, similar to 90% of the LIRGs have low Sersic indices (n &lt; 2.5, similar to disk-like galaxies) in the K-s-band, and that those disk-like LIRGs consist of similar to 60% of the whole disk-like sample above M-s &gt;= 3 x 10(10) M-circle dot. The z similar to 1 disk-like LIRGs are comparable to or similar to 20% smaller at the maximum in size compared to local disk-like galaxies in the same stellar mass range. When we examined rest-frame UV-optical morphologies using the HST/ACS images, the rest-frame B-band sizes of the z similar to 1 disk-like galaxies were found to be comparable to those of the local disk-like galaxies, as reported by previous studies on the size evolution of disk-like galaxies in the rest-frame optical band. By measuring color gradients (galaxy sizes as a function of wavelength) of the z similar to 1 and local disk-like galaxies, we found that the z similar to 1 disk-like galaxies have a 3-5 times steeper color gradient than the local ones. Our results indicate that (i) more than a half of the relatively massive disk-like galaxies at z similar to 1 are in violent star-formation epochs observed as LIRGs, and also (ii) that most of those LIRGs are constructing their fundamental disk structure vigorously. The high SFR density in the universe at z similar to 1 may be dominated by such star formation in the disk region in massive galaxies.

DOI： 10.1093/pasj/63.sp2.S363

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Language：English   Publishing type：Research paper (scientific journal)  

We present an IRAC 3.6+4.5 μm selected catalog in the Extended Groth Strip (EGS) containing photometry from the ultraviolet to the far-infrared and stellar parameters derived from the analysis of the multi-wavelength data. In this paper, we describe the method used to build coherent spectral energy distributions (SEDs) for all the sources. In a forthcoming companion paper, we analyze those SEDs to obtain robust estimations of stellar parameters such as photometric redshifts, stellar masses, and star formation rates. The catalog comprises 76,936 sources with [3.6] ≤ 23.75 mag (85% completeness level of the IRAC survey in the EGS) over 0.48 deg2. For approximately 16% of this sample, we are able to deconvolve the IRAC data to obtain robust fluxes for the multiple counterparts found in ground-based optical images. Typically, the SEDs of the IRAC sources in our catalog count with more than 15 photometric data points, spanning from the ultraviolet wavelengths probed by GALEX to the far-infrared observed by Spitzer, and going through ground- and space-based optical and near-infrared data taken with 2-8 m class telescopes. Approximately 95% and 90% of all IRAC sources are detected in the deepest optical and near-infrared bands. These fractions are reduced to 85% and 70% for S/N &gt
5 detections in each band. Only 10% of the sources in the catalog have optical spectroscopy and redshift estimations. Almost 20% and 2% of the sources are detected by MIPS at 24 and 70 μm, respectively. We also cross-correlate our catalog with public X-ray and radio catalogs. Finally, we present the Rainbow Navigator public Web interface utility, designed to browse all the data products resulting from this work, including images, spectra, photometry, and stellar parameters. © 2011 The American Astronomical Society. All rights reserved.

DOI： 10.1088/0067-0049/193/1/13

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Publishing type：Research paper (scientific journal)  

We present results from Submillimeter Array (SMA) 860 μm subarcsecond astrometry and multiwavelength observations of the brightest millimeter (S <SUB>1.1mm</SUB> = 8.4 mJy) source, SSA22-AzTEC1, found near the core of the SSA22 protocluster that is traced by Lyα-emitting galaxies at z = 3.09. We identify a 860 μm counterpart with a flux density of S <SUB>860 μm</SUB> = 12.2 ± 2.3 mJy and absolute positional accuracy that is better than 0farcs3. At the SMA position, we find radio-to-mid-infrared counterparts, whilst no object is found in Subaru optical and near-infrared deep images at wavelengths &lt;=1 μm (J &gt; 25.4 in AB, 2σ). The photometric redshift estimate, using flux densities at &gt;=24 μm, indicates z <SUB>phot</SUB> = 3.19<SUP>+0.26</SUP> <SUB>-0.35</SUB>, consistent with the protocluster redshift. We then model the near-to-mid-infrared spectral energy distribution (SED) of SSA22-AzTEC1, and find that the SED modeling requires a large extinction (A<SUB>V</SUB> ≈ 3.4 mag) of starlight from a stellar component with M <SUB>star</SUB> ~ 10<SUP>10.9</SUP> M <SUB>sun</SUB>, assuming z = 3.1. Additionally, we find a significant X-ray counterpart with a very hard spectrum (Γ<SUB>eff</SUB> = -0.34<SUP>+0.57</SUP> <SUB>-0.61</SUB>), strongly suggesting that SSA22-AzTEC1 harbors a luminous active galactic nuclei (AGNs; L<SUB>X</SUB> ≈ 3 × 10<SUP>44</SUP> erg s<SUP>-1</SUP>) behind a large hydrogen column (N <SUB>H</SUB> ~ 10<SUP>24</SUP> cm<SUP>-2</SUP>). The AGN, however, is responsible for only ~10% of the bolometric luminosity of the host galaxy, and therefore the star formation activity likely dominates the submillimeter emission. It is possible that SSA22-AzTEC1 is the first example of a protoquasar growing at the bottom of the gravitational potential underlying the SSA22 protocluster....

DOI： 10.1088/0004-637X/724/2/1270

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

We study the evolution of star formation activity of galaxies at 0.5 &lt
z &lt
3.5 as a function of stellar mass, using very deep NIR data taken with the Multi-Object Infrared Camera and Spectrograph on the Subaru telescope in the GOODS-North region. The NIR imaging data reach K ∼ 23-24 Vega magnitude and they allow us to construct a nearly stellar-mass-limited sample down to ∼109.5-10 M⊙ even at z ∼ 3. We estimated star formation rates (SFRs) of the sample with two indicators, namely, the Spitzer/MIPS 24 μm flux and the rest-frame 2800 Å luminosity. The SFR distribution at a fixed Mstar shifts to higher values with increasing redshift at 0.5 &lt
z &lt
3.5. More massive galaxies show stronger evolution of SFR at z ≳ 1. We found galaxies at 2.5 &lt
z &lt
3.5 show a bimodality in their SSFR distribution, which can be divided into two populations by a constant SSFR of ∼ 2 Gyr-1. Galaxies in the low-SSFR group have SSFRs of ∼ 0.5-1.0 Gyr-1, while the high-SSFR population shows ∼ 10 Gyr-1. The cosmic SFR density (SFRD) is dominated by galaxies with Mstar = 1010-11M⊙ at 0.5 &lt
z &lt
3.5, while the contribution of massive galaxies with M star = 1011-11.5 M⊙ shows a strong evolution at z &gt
1 and becomes significant at z ∼ 3, especially in the case with the SFR based on MIPS 24 μm. In galaxies with Mstar = 1010-11.5 M⊙, those with a relatively narrow range of SSFR (≲1 dex) dominates the cosmic SFRD at 0.5 &lt
z &lt
3.5. The SSFR of galaxies that dominate the SFRD systematically increases with redshift. At 2.5 &lt
z &lt
3.5, the high-SSFR population, which is relatively small in number, dominates the SFRD. Major star formation in the universe at higher redshift seems to be associated with a more rapid growth of stellar mass of galaxies. © 2010. The American Astronomical Society.

DOI： 10.1088/0004-637X/723/1/129

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present the results of near-infrared multi-object spectroscopic observations for 37 BzK-color-selected star-forming galaxies conducted with MOIRCS on the Subaru Telescope. The sample is drawn from the K-s-bandselected catalog of the MOIRCS Deep Survey in the GOODS-N region. About half of our samples are selected from the publicly available 24 mu m-source catalog of the Multiband Imaging Photometer for Spitzer on board the Spitzer Space Telescope. Ha emission lines are detected from 23 galaxies, of which the median redshift is 2.12. We derived the star formation rates (SFRs) from extinction-corrected Ha luminosities. The extinction correction is estimated from the spectral energy distribution (SED) fitting of multiband photometric data covering UV to near-infrared wavelengths. The Balmer decrement of the stacked emission lines shows that the amount of extinction for the ionized gas is larger than that for the stellar continuum. From a comparison of the extinction-corrected Ha luminosity and other SFR indicators, we found that the relation between the dust properties of stellar continuum and ionized gas is different depending on the intrinsic SFR (differential extinction). We compared SFRs estimated from extinction-corrected Ha luminosities with stellar masses estimated from SED fitting. The comparison shows no correlation between SFR and stellar mass. Some galaxies with stellar mass smaller than similar to 10(10) M-circle dot show SFRs higher than similar to 100 M-circle dot yr(-1). The specific SFRs (SSFRs) of these galaxies are remarkably high; galaxies which have SSFR higher than similar to 10(-8) yr(-1) are found in eight of the present sample. From the best-fit parameters of SED fitting for these high-SSFR galaxies, we find that the average age of the stellar population is younger than 100 Myr, which is consistent with the implied high SSFR. The large SFR implies the possibility that the high-SSFR galaxies significantly contribute to the cosmic SFR density of the universe at z similar to 2. When we apply the larger extinction correction for the ionized gas or the differential extinction correction, the total SFR density estimated from the H alpha-emission-line galaxies is 0.089-0.136 M-circle dot yr(-1) Mpc(-3), which is consistent with the total SFR densities in the literature. The metallicity of the high-SSFR galaxies, which is estimated from the N2 index, is larger than that expected from the mass-metallicity relation of UV-selected galaxies at z similar to 2 by Erb et al.

DOI： 10.1088/0004-637X/718/1/112

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present a population study of several types of galaxies within the protocluster surrounding the radio galaxy MRC 0316-257 at z similar to 3.1. In addition to the known population of Ly alpha emitters and [O iii] emitters, we use colour-selection techniques to identify protocluster candidates that are Lyman break galaxies (LBG) and Balmer break galaxies (BBGs). The radio galaxy field contains an excess of LBG candidates, with a surface density 1.6 +/- 0.3 times larger than found for comparable blank fields. This surface overdensity corresponds to an LBG volume overdensity of similar to 8 +/- 4. The BBG photometric redshift distribution peaks at the protocluster's redshift, but we detect no significant surface overdensity of BBG. This is not surprising because a volume overdensity similar to the LBGs would have resulted in a surface density of similar to 1.2 that found in the blank field. This could not have been detected in our sample. Masses and star formation rates of the candidate protocluster galaxies are determined using spectral energy distribution fitting. These properties are not significantly different from those of field galaxies. The galaxies with the highest masses and star formation rates are located near the radio galaxy, indicating that the protocluster environment influences galaxy evolution at z similar to 3. We conclude that the protocluster around MRC 0316-257 is still in the early stages of formation.

DOI： 10.1111/j.1365-2966.2010.16537.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present a universal linear correlation between the stellar mass and surface brightness (SB) of galaxies at 0.3 &lt; z &lt; 3, using a deep K-band-selected catalog in the GOODS-North region. The correlation has a nearly constant slope, independent of redshift and color of galaxies in the rest-z frame. Considering unresolved compact galaxies, the tight correlation gives a lower boundary of SB for a given stellar mass; lower SB galaxies are prohibited over the boundary. The universal slope suggests that the stellar mass in galaxies was built up over their cosmic histories in a similar manner irrelevant to galaxy mass, as opposed to the scenario that massive galaxies mainly accumulated their stellar mass by major merging. In contrast, SB shows a strong dependence on redshift for a given stellar mass. It evolves as similar to(1+ z)(-2.0 similar to- 0.8), in addition to dimming as (1+z)(4) by the cosmological expansion effect. The brightening depends on galaxy color and stellar mass. The blue population (rest-frame U - V &lt; 0), which is dominated by young and star-forming galaxies, evolves as similar to(1 + z)(-0.8 +/- 0.3) in the rest-V band. On the other hand, the red population (U - V &gt; 0) and the massive galaxies (M(*) &gt; 10(10) M(circle dot)) show stronger brightening, (1 + z)(-1.5 +/- 0.1). By comparison with galaxy evolution models, the phenomena are well understood by the pure luminosity evolution of galaxies out to z similar to 3.

DOI： 10.1088/0004-637X/709/2/741

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP SCIENCES S A  

We present a spectroscopic campaign to follow-up red colour-selected candidate massive galaxies in two high redshift proto-clusters surrounding radio galaxies. We observed a total of 57 galaxies in the field of MRC0943-242 (z = 2.93) and 33 in the field of MRC 1138-262 (z = 2.16) with a mix of optical and near-infrared multi-object spectroscopy.
We confirm two red galaxies in the field of MRC 1138-262 at the redshift of the radio galaxy. Based on an analysis of their spectral energy distributions, and their derived star formation rates from the Ha and observed frame 24 mu m flux, one object belongs to the class of dust-obscured star-forming red galaxies, while the other is evolved with little ongoing star formation. This result represents the first red and mainly passively evolving galaxy to be confirmed as companion galaxies in a z &gt; 2 proto-cluster. Both red galaxies in MRC 1138-262 are massive, of the order of 4-6 x 10(11) M(circle dot). They lie along a colour-magnitude relation which implies that they formed the bulk of their stellar population around z = 4.
In the MRC0943-242 field we find no red galaxies at the redshift of the radio galaxy but we do confirm the effectiveness of our JHK(s) selection of galaxies at 2.3 &lt; z &lt; 3.1, finding that 10 out of 18 (56%) of JHK(s)-selected galaxies whose redshifts could be measured fall within this redshift range. We also serendipitously identify an interesting foreground structure of 6 galaxies at z = 2.6 in the field of MRC0943-242. This may be a proto-cluster itself, but complicates any interpretation of the red sequence build-up in MRC 0943-242 until more redshifts can be measured.

DOI： 10.1051/0004-6361/200912868

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.1088/0004-637x/702/2/1393

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.1088/0004-637x/699/2/1354

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present the results of deep near-infrared imaging observations of the z = 3.1 proto-cluster region in the SSA 22a field taken by MOIRCS mounted on the Subaru Telescope. We observed a 21.7 arcmin(2) field to depths of J = 24.5, H = 24.3, and K = 23.9 (5 sigma). We examined the distribution of the K-selected galaxies at z similar to 3 by using a simple color cut for distant red galaxies (DRGs) as well as a photometric-redshift selection technique. The marginal density excess of DRGs and the photo-z selected objects were found around the two most luminous Ly alpha blobs (LABS). We investigated the correlation between the K-selected objects and the LABS, and found that several galaxies with stellar mass, M-* = 10(9)-10(11) M-circle dot, exist in the vicinity of LABS, especially around the two most luminous ones. We also found that 7 of the 8 LABS in the field have plausible K-s-band counterparts, and the sum of the stellar mass possibly associated with LABS correlates with their luminosity and surface brightness, which implies that the origin of Ly alpha emission may be closely correlated with their previous star-formation phenomena.

DOI： 10.1093/pasj/60.4.683

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.1086/527321

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present the first measurement of clustering properties of low-mass galaxies with a stellar mass down to M-* similar to 10(9)M(circle dot) at 1 &lt; z &lt; 4 in 24.4 arcmin(2) of the GOODS-North region with a depth of K-AB similar to 25. Luminous galaxies in the K-band have a larger correlation length than faint galaxies. For color-selected samples at 2 &lt; z &lt; 4, distant red galaxies with J-K &gt; 1.3 show a large bias of b similar to 7.2 +/- 1.3 on scales of up to theta similar to 100 '' or 3.1 comoving Mpc, while blue galaxies with 0.5 &lt; J-K &lt; 1.3 have a weak clustering signal on large scales, but a possible strong small-scale excess at theta &lt; 10 ''. For massive galaxies with M-* greater than or similar to 10(10)M(circle dot), we estimate the correlation length and bias to be r(0) similar to 4.5 h(-1) Mpc and b = 1.9-3.5, which are much larger than those of low-mass (M-* similar to 10(9)-10(10)M(circle dot)) galaxies. The comparison of our measurements with analytic CDM models constrains the properties of hosting dark halos, and indicates that the low-mass galaxies would be progenitors of galaxies with a typical luminosity of L less than or similar to L-* in the local Universe. The blue galaxies in low-mass samples are more strongly clustered in more massive halos with higher occupation numbers than low-mass red galaxies. This fact suggests an environment effect due to the halo mass on the star-formation activity at high-z.

DOI： 10.1093/pasj/59.6.1081

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Language：English   Publishing type：Research paper (scientific journal)  

We explore the evolved galaxy population in the proto-clusters around four high-z radio galaxies at based on wide-field near-infrared (NIR) imaging. Three of the four fields are known proto-clusters as demonstrated by overdensities of line-emitting galaxies at the same redshifts as the radio galaxies found by narrow-band surveys and spectroscopic follow-up observations. We imaged the fields of three targets (PKS 1138-262, USS 0943-242 and MRC 0316-257) to a depth of (Vega magnitude, 5σ) over a area centred on the radio galaxies with a new wide-field NIR camera, Multi-Object Infra-Red Camera and Spectrograph (MOIRCS), on the Subaru Telescope. Another target (USS 1558-003) was observed with Son of ISAAC on the New technology Telescope (NTT) to a depth of over a area. We apply colour cuts in and/or in order to exclusively search for galaxies located at high redshifts:. To the 5σ limiting magnitudes, we see a significant excess of NIR-selected galaxies by a factor of 2 to 3 compared to those found in the field of GOODS-South. The spatial distribution of these NIR-selected galaxies is not uniform and traces structures similar to those of emission-line galaxies, although the samples of NIR-selected galaxies and emitters show little overlap, from which we conclude that the former tend to be an evolved population with much higher stellar mass than the latter, young and active emitters. We focus on the NIR colour-magnitude sequence of the evolved population and find that the bright-end of the red sequence is well populated by but much less so in the proto-clusters. This may imply that the bright-end of the colour-magnitude sequence first appeared between and 2, an era coinciding with the appearance of sub-mm galaxies and the peak of the cosmic star formation rate. Our observations show that during the same epoch, massive galaxies are forming in high-density environments by vigorous star formation and assembly. © 2007 RAS.

DOI： 10.1111/j.1365-2966.2007.11739.x

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Language：English   Publishing type：Research paper (scientific journal)  

We report a discovery of possible large-scale structures around the RDCS J1252.9-2927 cluster at based on photometric redshifts. We carried out multiband wide-field imaging with Suprime-Cam on the Subaru Telescope and WFCAM on the United Kingdom Infrared Telescope (UKIRT). Our data cover an approximately field in and K bands. We apply a photometric redshift technique to extract galaxies at or near the cluster redshift. The distribution of photo-z selected galaxies reveals clumpy structures surrounding the central cluster. It seems that there is a large (&gt
20 Mpc) filamentary structure extending in the north-east-south-west direction. We compare the observed structure with an X-ray map and find that two of the four plausible clumps show significant X-ray emissions and one with a marginal detection, which strongly suggests that they are dynamically bound systems. Following the discovery of the possible large-scale structure, we carried out deeper SOFI Ks-band imaging with the New Technology Telescope on four plausible clumps. We construct the optical-to-near-infrared colour-magnitude diagrams of the galaxies in the clumps, and find that the colour-magnitude relation (CMR) of the red galaxies in the clumps is sharply truncated below. Few faint red galaxies are seen in these clumps. This suggests that the CMR first appears at the bright magnitudes and it extends to the fainter magnitudes with time, which is consistent with the 'downsizing' picture. Interestingly, the CMR of the main cluster has previously been shown to have a clear relation down to. This confirms our previous suggestion that the build-up of the CMR is delayed in low-density environments. All in all, we suggest that galaxies follow the 'environment-dependent downsizing' evolution. Massive galaxies in high-density environments first stop forming stars and become red. Less massive galaxies in less dense environments become red at later times. Based on a few assumptions, we predict that the brightest tip of the CMR appears at. © 2007 The Authors. Journal compilation © 2007 RAS.

DOI： 10.1111/j.1365-2966.2007.11671.x

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/58.6.951

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We use deep multiband optical and near-infrared data for four general fields, GOODS-South, HDF-North/South, and IRAC UDF in GOODS-North to investigate the evolution of the observed rest-frame U - V color of field galaxies as a function of the stellar mass evaluated by fitting the galaxy spectral models to the observed broadband SEDs. In these four fields, the U - V color distributions of the galaxies at each mass and redshift interval are very similar. We found that at 0.3 &lt; z &lt; 2.7, more massive galaxies always tend to have a redder U - V color. High- and low-mass galaxies exhibit quite different color evolutions. As seen in our previous study in HDF-N, the color distribution of low-mass ( M star less than or similar to 3 x 10(9) M-circle dot) galaxies becomes significantly bluer with an increase in the redshift. This evolution of the average color can be explained by a constant star formation rate model with z(form) similar to 4. On the other hand, the average color of high-mass galaxies ( M star greater than or similar to 3 x 10(10) M-circle dot) evolves more strongly at high redshifts. Such mass-dependent color distribution and its evolution indicate that galaxies with a larger stellar mass appear to have shorter star formation timescales, and on average they form the larger fraction of their stars in the earlier epoch.

DOI： 10.1086/506428

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Language：English   Publishing type：Research paper (scientific journal)  

We report the discovery of protocluster candidates around high-redshift radio galaxies at z ∼ 2.5 on the basis of clear statistical excess of colour-selected galaxies around them seen in the deep near-infrared imaging data obtained with CISCO on the Subaru Telescope. We have observed six targets, all at similar redshifts at z ∼ 2.5, and our data reach J = 23.5, H = 22.6 and K = 21.8 (5σ) and cover a 1.6 × 1.6 arcmin 2 field centred on each radio galaxy. We apply colour cuts in JHK bands in order to exclusively search for galaxies located at high redshifts, z &gt
2. Over the magnitude range of 19.5 &lt
K &lt
21.5, we see a significant excess of red galaxies with J - K &gt
2.3 by a factor of 2 around the combined radio galaxies fields compared to those found in the general field of the Great Observatories Origins Deep Survey-South (GOODS-S). The excess of galaxies around the radio galaxies fields becomes more than a factor of 3 around 19.5 &lt
K &lt
20.5 when the two-colour cuts are applied with JHK bands. Such overdensity of the colour-selected galaxies suggests that those fields tend to host high-density regions at high redshifts, although there seems to be the variety of the density of the colour-selected galaxies in each field. In particular, two radio galaxies fields out of the six observed fields show very strong density excess and these are likely to be protoclusters associated with the radio galaxies which would evolve into rich clusters of galaxies dominated by old passively evolving galaxies. © 2006 RAS.

DOI： 10.1111/j.1365-2966.2006.10704.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

We obtained the number counts and the rest-frame B-band luminosity function of color-selected old passively evolving galaxies (OPEGs) at z = 1 with very high statistical accuracy using a large and homogeneous sample of about 4000 such objects with z′ &lt
25 detected in an area of 1.03 deg2 in the Subaru/XMM-Newton Deep Survey (SXDS) field. Our selection criteria are defined on the i′ - z′ and R - z′ color-magnitude plane so that OPEGs at z = 0.9-1.1 with formation redshift zf = 2-10 are properly sampled with minimum contamination by other populations. The limiting magnitude corresponds to the luminosity of galaxies with M* + 3 at z = 0. We made pilot redshift observations for 99 OPEG candidates with 19 &lt
z′ &lt
22 and found that at least 78% (73 of 93) of the entire sample, or 95% (73 of 77) of those whose redshifts were obtained, indeed lie between z = 0.87 and 1.12, and most of their spectra show a continuum break and strong Ca H and K lines, indicating that these objects are indeed dominated by the old stellar populations. The relationship between the observed redshift and the color closely follows the models used in defining the selection criteria in a consistent manner. We found that the surface number density of OPEGs varies by 10%-30% of the average of the entire sample from field to field even at a 30′ scale and that the poorest field, SXDS-South, has only 65% of that of the richest one, SXDS-East. We then compared our results with the luminosity functions of the color- or morphologically selected early-type galaxies at z = 0, taking the evolutionary factor into account, and found that the number density of old passive galaxies with ∼M* magnitude at z ∼ 1 averaged over the SXDS area is 40%-60% that of equivalently red galaxies and 60%-85% that of morphologically selected E/S0 galaxies at z = 0 depending on their luminosity evolution. It is revealed that more than half, but not all, of the present-day early-type galaxies had already evolved into quiescent passive galaxies at z = 1. © 2005. The American Astronomical Society. All rights reserved.

DOI： 10.1086/496954

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：UNIV CHICAGO PRESS  

Using very deep Subaru K'-band imaging and archival Hubble Space Telescope WFPC2/NICMOS data of the Hubble Deep Field-North, we investigate the evolution of the stellar mass, color, and morphology of galaxies to z similar to 3. We mainly examine the rest-frame U-V color distribution of galaxies as a function of stellar mass. At 0.3 less than or similar to z less than or similar to 2, galaxies seem to be divided into the two populations at around the stellar mass of similar to5 x 10(9) M.. The low-mass galaxies have relatively bluer rest-frame U-V color, and their color does not show a clear correlation with stellar mass over the range 10(8) to 5 x 10(9) M.. On the other hand, at higher mass, the more massive galaxies tend to have redder U-V color. The average U-V color of the low-mass galaxies gradually becomes bluer with redshift, from U-V similar to 0.2 at z similar to 0.5 to U-V similar to -0.2 at z similar to 2. However, the correlation between the stellar mass and rest-frame U-V color of the high-mass population does not seem to change significantly between z similar to 0.3 and z similar to 2. The morphological distribution shows that at z less than or similar to 1, the low- mass population is dominated by disk galaxies, while the fraction of early-type galaxies is larger in the high-mass population. At 1 &lt; z &lt; 2, although the fraction of irregular galaxies increases, a similar trend is observed. At z &gt; 2, it is seen that more massive galaxies tend to have redder U-V color over the range 10(9)-10(10) M., although we can only sample galaxies with stellarmass larger than similar to1 x 10(9) M.. These results suggest that the star formation history of galaxies depends greatly on their stellar mass. The low- mass population is likely to have a relatively long star formation timescale, and under the assumption of a constant star formation rate, their formation redshifts do not seem to be much higher than z similar to 2. At stellar masses larger than similar to5 x 10(9) M., there must be some mechanism that suppresses star formation in galaxies at 0 &lt; z &lt; 2.

DOI： 10.1086/425957

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Language：English   Publishing type：Research paper (scientific journal)  

We use the deep wide-field optical imaging data of the Subaru/XMM-Newton Deep Survey to discuss the luminosity- (mass-)dependent galaxy colours down to z′ = 25.0 (5 × 10 9 h 70 -2 M ⊙) for z ∼ 1 galaxies in colour-selected high-density regions. We find an apparent absence of galaxies on the red colour-magnitude sequence below z′ ∼ 24.2, corresponding to ∼M* + 2 (∼ 10 10 M ⊙) with respect to passively evolving galaxies at z ∼ 1. Galaxies brighter than M* -0.5 (8 × 10 10 M ⊙), however, are predominantly red passively evolving systems, with few blue star-forming galaxies at these magnitudes. This apparent age gradient, where massive galaxies are dominated by old stellar populations while less massive galaxies have more extended star formation histories, supports the 'down-sizing' idea where the mass of galaxies hosting star formation decreases as the Universe ages. Combined with the lack of evolution in the shape of the stellar mass function for massive galaxies since at least z ∼ 1, it appears that galaxy formation processes (both star formation and mass assembly) should have occurred in an accelerated way in massive systems in high-density regions, while these processes should have been slower in smaller systems. This result provides an interesting challenge for modern cold dark matter based galaxy formation theories which predict later formation epochs of massive systems, commonly referred to as 'bottom-up'.

DOI： 10.1111/j.1365-2966.2004.07711.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BLACKWELL PUBLISHING LTD  

Despite extensive observational efforts, a convincing optical/infrared identification of the brightest submm source in the Hubble Deep Field, HDF 850.1, has remained elusive after almost four years. This failure is all the more notable given the availability of supporting multifrequency data of unparalleled depth, and subarcsec positional accuracy for the submm/mm source. Consequently, HDF 850.1 has become a test case for the possibility that the most violently star-forming objects in the Universe are too red and/or distant to be seen in the deepest optical images.
Here we report the discovery of the galaxy counterpart of HDF 850.1. This object has been revealed by careful analysis of a new, deep K' image of the HDF obtained with the Subaru 8.2-m telescope. Its reality is confirmed by a similar analysis of the HST NICMOS F160W image of the same region. This object is extremely faint (K similar or equal to 23.5), clumpy (on subarcsec scales) and very red (I - K &gt; 5.2; H - K = 1.4 +/- 0.35). The likelihood that it is the correct galaxy counterpart is strongly reinforced by a reanalysis of the combined MERLIN+VLA 1.4-GHz map of the field, which provides a new radio detection of HDF 850.1 only 0.1 arcsec from the new near-infrared counterpart, and with sufficient positional accuracy to exclude all previously considered alternative optical candidates.
We have calculated new confidence limits on the estimated redshift of HDF 850.1 in the light of the new radio detection, and find z = 4.1 +/- 0.5. We have also determined the scalelength, and hence estimated the mass of the apparently nearby (0.5 arcsec distant) z similar or equal to 1 elliptical galaxy 3-586.0. From this we calculate that the flux density of HDF 850.1 has been boosted by a factor of similar or equal to3 through gravitational lensing by this intervening elliptical, consistent with predictions that a small but significant fraction of blank-field submm sources are lensed by foreground galaxies. We discuss the wider implications of these results for the submm population and cosmic star formation history.

DOI： 10.1111/j.1365-2966.2004.07700.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Hyper extremely red objects (HEROs) are objects that are very red in near-IR colors (J-K greater than or similar to 3). They are speculated to be intrinsically red galaxies at z greater than or similar to 2 or Lyman break galaxies at z &gt; 10. We report the discovery of a HERO in the field that includes a known radio galaxy, 53W002, and a possible cluster of galaxies both at z = 2.39. The HERO, which we name HERO J171411.91+501541.8, or 53W002-HERO1 for brevity, is visible in the Hubble Space Telescope Near-Infrared Camera and Multi-Object Spectrometer H-band data and deep K'-band data from the Subaru Telescope (K' similar or equal to 21.5 mag) but not visible in B-, V-, I-, and J-band images (J-K &gt; 4.45, 2 sigma). Its spectral energy distribution is consistent with that of a dusty star- forming or old galaxy at z similar or equal to 2.4, which may suggest that 53W002-HERO1 is a member of the group of galaxies associated with 53W002. Alternatively, the HERO could be at z similar or equal to 12.5, if its red color is due to the redshifted Lyman break. If 53W002- HERO1 is an old galaxy at z similar to 2.4, the implied stellar age is similar to2- 3 Gyr, meaning that stars in the HERO formed at the reionization epoch of z greater than or similar to 10.

DOI： 10.1086/344475

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：UNIV CHICAGO PRESS  

We have obtained a new high-resolution K'-band image of the central region of the rich X-ray cluster RX J0848.9+4452 at z = 1.26. We found that the brightest cluster galaxy (BCG) in the cluster is clearly separated into two distinct objects. Whereas the optical to near-infrared colors of the objects are consistent with the predictions of passive evolution models for galaxies formed at high redshift, the luminosities of the two galaxies are both considerably fainter than predicted by passive evolution of BCGs in low- and intermediate-redshift clusters. We argue that this is evidence of an ongoing merger of normal cluster elliptical galaxies to form the dominant galaxy in the core of RX J0848.9+4452. The two galaxies appear to point toward the nearby cluster ClG J0848+4453 and are aligned with the outer X-ray contour of their parent cluster, supporting a model of BCG formation by collimated infall along the surrounding large-scale structure.

DOI： 10.1086/344400

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We discuss the properties of galaxies around the radio galaxy 3C 324 at z = 1.2 based on B VRI K' multi-band imaging data. We have applied a photometric-redshift technique to objects in the 3C 324 field, and identified 35 objects as plausible cluster members. We have found that red and luminous members are concentrated in a small region enclosed by a circle of 40" radius (0.33 Mpc at z = 1.2 for Omega(0) = 0.3, lambda(0) = 0.7, H-0 = 70 kms(-1) Mpc(-1) cosmology) from the 3C 324 galaxy. The 3C 324 cluster is probably much more compact in size compared with the local clusters. We constructed a V-band luminosity function of the cluster members and fitted a Schechter function, and found the characteristic magnitude to be K-AB'* = 20.2 +/- 0.6. This value is consistent with the extrapolation of the pure AB passive evolution seen for z &lt; I clusters. We have identified eight bright galaxies which form a red color-magnitude sequence. The slope of the sequence is consistent with the passive evolution model down to K-AB' &lt; 22; we also A found that there is no clear age variation in these bright red galaxies. However, seven out of these eight galaxies exhibit a significant excess in the rest UV light with respect to the passive evolution model. This may suggest that the massive early-type galaxies in this high-redshift cluster are still forming stars to some extent. We have confirmed a truncation of the color-magnitude sequence at K-AB' similar to 22; faint passively-evolving, galaxies may not yet be present in this cluster at z similar to 1.2. The overall color distribution of the cluster members, selected by the photometric redshift technique, is found to be very broad. We derived the fraction of blue galaxies in this cluster following a definition of Butcher and Oemler (1984, AAA 038.160.068), and obtained f(B) = 0.39 +/- 0.28, which is higher than that for z &lt; 1 clusters. This indicates that the star-formation activity of this cluster is, on the average, higher than that of lower redshift counterparts.

DOI： 10.1093/pasj/53.6.1139

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Using the HST WFPC2/NICMOS archival data of the Hubble Deep Field North, we constructed a nearly complete sample of the M-V &lt; -20 (similar to L* + 1) galaxies to z = 2, and investigate when the Hubble sequence appeared, namely, the evolution of the morphology, colors, and the comoving number density of the sample. Even if taking into account the uncertainty of the photometric redshift technique, the number density of relatively bright bulge-dominated galaxies in the HDF-N decreases significantly at z &gt; 1, and their rcst-frame U - V color distribution is wide-spread over 0.5 &lt; z &lt; 2. On the other hand, while the number density of both disk-dominated and irregular galaxies does not show a significant change at 0.5 &lt; z &lt; 2, their distribution of the rest-frame U - V color alters at z similar to 1.5; there is no relatively red (rest U - V greater than or similar to 0.3) galaxies at z &gt; 1.5, while a significant fraction of these red disk-dominated or irregular galaxies exist at z &lt; 1.5. These results suggest that the significant evolution of the Hubble sequence, which is seen in the present Universe, occurs at 1 &lt; z &lt; 2.

DOI： 10.1093/pasj/53.5.833

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astronomical Society of Japan  

We present the results of deep K′ and J-band imaging of the field of a proto-cluster region near the radio galaxy 53W002 at z = 2.390 with the Subaru Telescope. The data were analyzed together with deep optical and near-infrared (NIR) images taken with the Hubble Space Telescope to investigate the properties of ten optically compact emission-line galaxies and candidates. Excluding the three objects which may contain active galactic nuclei, many are faint or undetected at K′ (λres ≈ 6000Å), and are therefore revealed to be intrinsically small starbursting objects. On the other hand, we detect few objects with colors and magnitudes expected for quiescent massive galaxies at z = 2.4 in the field.

DOI： 10.1093/pasj/53.6.1119

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/52.1.43

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We investigate the K-band luminosity distribution of galaxies in the region of clusters at z similar to 1.2 near to the radio galaxy 3C 324. The imaging data;were obtained during the commissioning period of the Subaru telescope. There is a significant excess of the surface number density of the galaxies with K = 17-20 mag in the region within similar to 40 " from 3C 324. At this bright end, the measured luminosity distribution shows a drop, which can be represented by the exponential cut off of the Schechter-function formula; the best-fitted value of the characteristic magnitude, K*, is similar to 18.4 +/- 0.8. This measurement follows the evolutionary trend of the K* of the rich clusters observed at an intermediate redshift, which is consistent with passive evolution models with a formation redshift z(f) greater than or similar to 2. At K greater than or similar to 20 mag, however, the excess of the galaxy surface density in the region of the clusters decreases abruptly, which may imply that the luminosity function of the cluster galaxies has a negative slope at the faint end. This may imply strong luminosity segregation between the inner and outer parts of the clusters, or some deficit of faint galaxies in the cluster central region of the cluster.

DOI： 10.1093/pasj/52.1.53

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Astronomical Society of Japan  

We have investigated the optical and near-infrared colors of K′-selected galaxies in clusters at z ∼ 1.2 near to the radio galaxy 3C 324 using images obtained with the Subaru telescope and archival HST data. The distribution of colors of the galaxies in the cluster region is found to be fairly broad, and it may imply significant scatter in their star-formation histories, although the effect of contamination of field galaxies is uncertain. The red sequence of galaxies whose R - K colors are consistent with passive evolution models for old galaxies is found to be truncated at K′ ∼ 20 mag, and there are few fainter galaxies with similar red colors in the cluster region. We find that the bulge-dominated galaxies selected by quantitative morphological classification form a broad sequence in the color - magnitude diagram, whose slope is much steeper than that expected from metallicity variations within a passively evolving coeval galaxy population. We argue that the observed color - magnitude sequence can be explained by metallicity and age variations, and the fainter galaxies with K′ &gt
20 mag may be 1-2 Gyr younger than the brighter galaxies. Some spatial segregation of the color and K′-band luminosity is seen in the sky distribution
the redder and the brighter objects tend to be located near 3C 324.

DOI： 10.1093/pasj/52.1.61

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We investigated the color and morphology of optically selected galaxies in the region of clusters at z similar to 1.2 near to the radio galaxy 3C 324 using archived data taken with the Hubble Space Telescope. The faint galaxies selected at the HST F702W band that contribute to the surface-density excess of the region have wide ranges of color, size, and morphology, which are not likely to be due to contamination by foreground galaxies. Namely, the rest-frame ultraviolet emission properties of the galaxies in the clusters are not very homogeneous; various amounts of star-formation activity may occur in a significant fraction of them. Although our analysis is purely statistical, we find that typical star-forming galaxies with blue colors have a relatively late-type morphology compared to the red quiescent population in the systems.

DOI： 10.1093/pasj/51.5.719

Web of Science

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J-GLOBAL

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J-GLOBAL

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Language：English   Publisher：ASTRONOMICAL SOC PACIFIC  

Web of Science

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Language：Japanese  

CiNii Books

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Language：Japanese  

CiNii Books

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