Masaru Kajisawa

The Subaru/XMM-Newton Deep Survey (SXDS) - II. Optical Imaging and Photometric Catalogs

We present multiYwave band optical imaging data obtained from observations of the Subaru/XMM-Newton Deep Survey (SXDS). The survey field, centered at R:A: ¼ 02 h 18 m 00 s , decl: ¼� 05 � 00 0 00 00 , has been the focus of a wide range of multiwavelength observing programs spanning from X-ray to radio wavelengths. A large part of the optical imaging observations are carried out with Suprime-Cam on Subaru Telescope at Mauna Kea in the course of Subaru Telescope ‘‘Observatory Projects.’’ This paper describes our optical observations, data reduction and analysis procedures employed, and the characteristics of the data products. A total area of 1.22 deg 2 is covered in five contiguous subfields,eachof whichcorrespondstoasingleSuprime-Camfieldof view(� 34 0 ; 27 0 ),infivebroadbandfilters,B, V,Rc,i 0 ,andz 0 ,tothedepthsof B ¼ 28:4,V ¼ 27:8,Rc ¼ 27:7,i 0 ¼ 27:7,andz 0 ¼ 26:6,respectively(AB,3 � , � ¼ 2 00 ). The data are reduced and compiled into five multiYwave band photometric catalogs, separately for each SuprimeCampointing.Thei 0 -bandcatalogscontainabout900,000objects,makingtheSXDScatalogsoneof thelargestmultiY wavebandcatalogsincorrespondingdepthandareacoverage.TheSXDScatalogscanbeusedforanextensiverangeof astronomicalapplicationssuchasthenumberdensityof theGalactichalostarstothelarge-scalestructuresatthedistant universe. The number counts of galaxies are derived and compared with those of existing deep extragalactic surveys. The optical data, the source catalogs, and configuration files used to create the catalogs are publicly available via the SXDS Web page (http://www.naoj.org/Science/SubaruProject/SXDS/index.html). Subject headingg cosmology: observations — galaxies: evolution — galaxies: formation — galaxies: photometry — large-scale structure of universe

Down‐sizing in galaxy formation at z∼ 1 in the Subaru/XMM–Newton Deep Survey (SXDS)

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 −2 70 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 ‘downsizing’ 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 highdensity 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’.

The first appearance of the red sequence of galaxies in proto‐clusters at 2 ≲z≲ 3

We explore the evolved galaxy population in the proto-clusters around four high-z radio galaxies at 2 ≤ z ≤ 3 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 K s ∼ 22 (Vega magnitude, 5σ) over a 4 x 7 arcmin 2 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 K s = 20.5 (5σ) over a 5 x 5 arcmin 2 area. We apply colour cuts in J-K s and/or JHK s in order to exclusively search for galaxies located at high redshifts: z > 2. 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 (M stars > 10 11 M ⊙ ) of the red sequence is well populated by z ∼ 2 but much less so in the z ∼ 3 proto-clusters. This may imply that the bright-end of the colour-magnitude sequence first appeared between z = 3 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.

The FMOS-COSMOS Survey of Star-forming Galaxies at z ~ 1.6. I. Hα-based Star Formation Rates and Dust Extinction

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 < z < 1.7. The high-resolution mode is implemented to detect Hα in emission between 1.6-1.8 μm with f Hα gsim 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 lsim A Hα lsim 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 E star(B – V)/E neb(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.

Evolution of galaxies and their environments at z = 0.1-3 in COSMOS

Large-scale structures (LSSs) out to z 0.8, the SFR density is uniformly distributed over all environmental density percentiles, while at lower redshifts the dominant contribution is shifted to galaxies in lower density environments.

MOIRCS Deep Survey. IV. Evolution of Galaxy Stellar Mass Function Back to z ~ 3

We use very deep near-infrared (NIR) imaging data obtained in MOIRCS Deep Survey (MODS) to investigate the evolution of the galaxy stellar mass function back to z ~ 3. The MODS data reach J = 24.2, H = 23.1, and K = 23.1 (5σ, Vega magnitude) over 103 arcmin2 (wide) and J = 25.1, H = 23.7, and K = 24.1 over 28 arcmin2 (deep) in the GOODS-North region. The wide and very deep NIR data allow us to measure the number density of galaxies down to low stellar mass (109-1010 M ☉) even at high redshift with high statistical accuracy. The normalization of the mass function decreases with redshift, and the integrated stellar mass density becomes ~8%-18% of the local value at z ~ 2 and ~4%-9% at z ~ 3, which are consistent with results of previous studies in general fields. Furthermore, we found that the low-mass slope becomes steeper with redshift from α ~ –1.3 at z ~ 1 to α ~ –1.6 at z ~ 3 and that the evolution of the number density of low-mass (109-1010 M ☉) galaxies is weaker than that of M* (~1011 M ☉) galaxies. This indicates that the contribution of low-mass galaxies to the total stellar mass density has been significant at high redshift. The steepening of the low-mass slope with redshift is an opposite trend expected from the stellar mass dependence of the specific star formation rate reported in previous studies. The present result suggests that the hierarchical merging process overwhelmed the effect of the stellar mass growth by star formation and was very important for the stellar mass assembly of these galaxies at 1 z 3.

The FMOS-Cosmos Survey of Star-Forming Galaxies at z ~ 1.6 II. The Mass-Metallicity Relation and the Dependence on Star Formation Rate and Dust Extinction

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 (~10^(11) 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.

UV-TO-FIR ANALYSIS OF SPITZER/IRAC SOURCES IN THE EXTENDED GROTH STRIP. II. PHOTOMETRIC REDSHIFTS, STELLAR MASSES, AND STAR FORMATION RATES

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 μ 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] ≤ 23.75 (85% completeness level of the IRAC survey) over 0.48 deg^2. The typical photometric redshift accuracy is ∆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 μ 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 ≳1.5 observed when only MIPS 24 μ 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.

UV-TO-FIR ANALYSIS OF SPITZER/IRAC SOURCES IN THE EXTENDED GROTH STRIP. I. MULTI-WAVELENGTH PHOTOMETRY AND SPECTRAL ENERGY DISTRIBUTIONS

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 deg^2. 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 > 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.

MOIRCS DEEP SURVEY. VI. NEAR-INFRARED SPECTROSCOPY OF K-SELECTED STAR-FORMING GALAXIES AT z ∼ 2*

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 Ks -band-selected catalog of the MOIRCS Deep Survey in the GOODS-N region. About half of our samples are selected from the publicly available 24 ?m-source catalog of the Multiband Imaging Photometer for Spitzer on board the Spitzer Space Telescope. H? 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 H? 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 H? 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 H? 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 ~1010 M ? show SFRs higher than ~100 M ? yr?1. The specific SFRs (SSFRs) of these galaxies are remarkably high; galaxies which have SSFR higher than ~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 ~ 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?-emission-line galaxies is 0.089-0.136 M ? 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 ~ 2 by Erb et al.