Tadafumi Takata

The Subaru/XMM-Newton Deep Survey (SXDS). IV. Evolution of Lyα Emitters from z = 3.1 to 5.7 in the 1 deg2 Field: Luminosity Functions and AGN*

We present luminosity functions (LFs) and various properties of Lyα emitters (LAEs) at z = 3.1, 3.7, and 5.7, in a 1 deg2 sky of the Subaru/XMM–Newton Deep Survey (SXDS) Field. We obtain a photometric sample of 858 LAE candidates based on deep Subaru Suprime-Cam imaging data and a spectroscopic sample of 84 confirmed LAEs from Subaru FOCAS and VLT VIMOS spectroscopy in a survey volume of ~106 Mpc3 with a limiting Lyα luminosity of ~3 × 1042 ergs s−1. We derive the LFs of the Lyα and UV continuum (1500 A) for each redshift, taking into account the statistical error and the field-to-field variation. We find that the apparent Lyα LF shows no significant evolution between z = 3.1 and 5.7 within factors of 1.8 and 2.7 in L* and *, respectively. On the other hand, the UV LF of LAEs increases from z = 3.1 to 5.7, indicating that galaxies with Lyα emission are more common at earlier epochs. We identify six LAEs with AGN activities from our spectra combined with VLA, Spitzer, and XMM-Newton data. Among the photometrically selected LAEs at z = 3.1 and 3.7, only 1% show AGN activities, while the brightest LAEs with log L(Ly α) 43.4–43.6 ergs s−1 appear to always host AGNs. Our LAEs are bluer in UV-continuum color than dropout galaxies, suggesting lower extinction and/or younger stellar populations. Our stacking analyses provide upper limits to the radio luminosity and the fHe II/fLyα line fraction and constrain the hidden star formation (+low-luminosity AGN) and the primordial population in LAEs.

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

Radio imaging of the Subaru/XMM-Newton Deep Field -I. The 100-μJy catalogue, optical identifications, and the nature of the faint radio source population

We describe deep radio imaging at 1.4 GHz of the 1.3-deg 2 Subaru/XMM-Newton Deep Field (SXDF), made with the Very Large Array in B and C configurations. We present a radio map of the entire field, and a catalogue of 505 sources covering 0.8 deg 2 to a peak flux density limit of 100 μJy. Robust optical identifications are provided for 90 per cent of the sources, and suggested identifications are presented for all but 14 (of which seven are optically blank, and seven are close to bright contaminating objects). We show that the optical properties of the radio sources do not change with flux density, suggesting that active galactic nuclei (AGN) continue to contribute significantly at faint flux densities. We test this assertion by cross-correlating our radio catalogue with the X-ray source catalogue and conclude that radio-quiet AGN become a significant population at flux densities below 300 μJy, and may dominate the population responsible for the flattening of the radio source counts if a significant fraction of them are Compton-thick.

Asphericity in Supernova Explosions from Late-Time Spectroscopy

Core-collapse supernovae (CC-SNe) are the explosions that announce the death of massive stars. Some CC-SNe are linked to long-duration gamma-ray bursts (GRBs) and are highly aspherical. One important question is to what extent asphericity is common to all CC-SNe. Here we present late-time spectra for a number of CC-SNe from stripped-envelope stars and use them to explore any asphericity generated in the inner part of the exploding star, near the site of collapse. A range of oxygen emission-line profiles is observed, including a high incidence of double-peaked profiles, a distinct signature of an aspherical explosion. Our results suggest that all CC-SNe from stripped-envelope stars are aspherical explosions and that SNe accompanied by GRBs exhibit the highest degree of asphericity.

Hyper Suprime-Cam

Hyper Suprime-Cam (HSC) is an 870 Mega pixel prime focus camera for the 8.2 m Subaru telescope. The wide field corrector delivers sharp image of 0.25 arc-sec FWHM in r-band over the entire 1.5 degree (in diameter) field of view. The collimation of the camera with respect to the optical axis of the primary mirror is realized by hexapod actuators whose mechanical accuracy is few microns. As a result, we expect to have seeing limited image most of the time. Expected median seeing is 0.67 arc-sec FWHM in i-band. The sensor is a p-ch fully depleted CCD of 200 micron thickness (2048 x 4096 15 μm square pixel) and we employ 116 of them to pave the 50 cm focal plane. Minimum interval between exposures is roughly 30 seconds including reading out arrays, transferring data to the control computer and saving them to the hard drive. HSC uniquely features the combination of large primary mirror, wide field of view, sharp image and high sensitivity especially in red. This enables accurate shape measurement of faint galaxies which is critical for planned weak lensing survey to probe the nature of dark energy. The system is being assembled now and will see the first light in August 2012.

Rest-Frame Optical Spectroscopic Classifications for Submillimeter Galaxies

We report the results of a systematic near-IR spectroscopic survey using the Subaru, VLT, and Keck Telescopes of a sample of high-redshift ULIRGs mainly composed of submillimeter-selected galaxies. Our observations span the rest-frame optical range containing nebular emission lines such as Hβ, [O III] λλ4959, 5007, and [O II] λ3727, which are essential for making robust diagnostics of the physical properties. Using the Hα/Hβ emission line ratios, we derive internal extinction estimates for these galaxies similar to those of local ULIRGs: A_V ~ 2.9 ± 0.5. Correcting the Hα estimates of the star formation rate for dust extinction results in rates that are consistent with those estimated from the far-IR luminosity. The majority (>60%) of our sample show spectral features characteristic of AGNs (although this partially reflects an observational bias), with ~65% exhibiting broad Balmer emission lines. A proportion of these sources show relatively low [O III] λ5007/Hβ line ratios, which are similar to those of narrow-line Seyfert 1 galaxies, suggesting low-mass black holes that are rapidly growing. In the subsample of our survey with both [O III] λ5007 and hard X-ray coverage, at least ~60% show an excess of [O III] λ5007 emission, by a factor of 5-10, relative to the hard X-ray luminosity compared to the correlation between these two properties seen in Seyfert galaxies and QSOs locally. From our spectral diagnostics, we propose that the strong [O III] λ5007 emission in these galaxies arises from shocks in dense gaseous regions. Due to sensitivity and resolution limits, our sample is biased to strong-line emitters and hence our results do not yet provide a complete view of the physical properties of the whole high-redshift ULIRG population.

Spatial correlation between submillimetre and Lyman-α galaxies in the SSA 22 protocluster

Lyman-α emitters are thought to be young, low-mass galaxies with ages of ∼108 yr (refs 1, 2). An overdensity of them in one region of the sky (the SSA 22 field) traces out a filamentary structure in the early Universe at a redshift of z ≈ 3.1 (equivalent to 15 per cent of the age of the Universe) and is believed to mark a forming protocluster. Galaxies that are bright at (sub)millimetre wavelengths are undergoing violent episodes of star formation, and there is evidence that they are preferentially associated with high-redshift radio galaxies, so the question of whether they are also associated with the most significant large-scale structure growing at high redshift (as outlined by Lyman-α emitters) naturally arises. Here we report an imaging survey of 1,100-μm emission in the SSA 22 region. We find an enhancement of submillimetre galaxies near the core of the protocluster, and a large-scale correlation between the submillimetre galaxies and the low-mass Lyman-α emitters, suggesting synchronous formation of the two very different types of star-forming galaxy within the same structure at high redshift. These results are in general agreement with our understanding of the formation of cosmic structure.

Evolution of Stellar-to-Halo Mass Ratio at z=0-7 Identified by Clustering Analysis with the Hubble Legacy Imaging and Early Subaru/Hyper Suprime-Cam Survey Data

We present clustering analysis results from 10,381 Lyman break galaxies (LBGs) at z~ 4-7, identified in the Hubble legacy deep imaging and new complimentary large-area Subaru/Hyper Suprime-Cam data. We measure the angular correlation functions (ACFs) of these LBGs at z~4, 5, 6, and 7, and fit these measurements using halo occupation distribution (HOD) models that provide an estimate of halo masses, M_h~(1-20)x10^11 Msun. Our M_h estimates agree with those obtained by previous clustering studies in a UV-magnitude vs. M_h plane, and allow us to calculate stellar-to-halo mass ratios (SHMRs) of LBGs. By comparison with the z~0 SHMR, we identify evolution of the SHMR from z~0 to z~4, and z~4 to z~7 at the >98% confidence levels. The SHMR decreases by a factor of ~2 from z~0 to 4, and increases by a factor of ~4 from z~4 to 7. We compare our SHMRs with results of a hydrodynamic simulation and a semi-analytic model, and find that these theoretical studies do not predict the SHMR increase from z~4 to 7. We obtain the baryon conversion efficiency (BCE) of LBGs at z~4, and find that the BCE increases with increasing dark matter halo mass. Finally, we compare our clustering+HOD estimates with results from abundance matching techniques, and conclude that the M_h estimates of the clustering+HOD analyses agree with those of the simple abundance matching within a factor of 3, and that the agreement improves when using more sophisticated abundance matching techniques that include subhalos, incompleteness, and/or evolution in the star formation and stellar mass functions.

Search and Redshift Survey for IRAS Galaxies behind the Milky Way and Structure of the Local Void

This is the third and final paper of our systematic visual search for IRAS galaxies behind the Milky Way at |b| ≤ 15°. This paper presents a catalog of 950 IRAS galaxies with 60 μm flux densities larger than 0.6 Jy located between l = 0° and 150°, of which 293 are newly identified by this search. We made a redshift survey for the identified galaxies and obtained new redshift data of 171 galaxies. We also present newly measured redshifts of 27 IRAS galaxies between l = 150° and 225° at |b| ≤ 15°. In this paper we studied the structure of the Local void using IRAS galaxies and galaxies from the Third Reference Catalogue of Bright Galaxies in the region l = 30°-120° and b = -50° to +30°. The center of the Local void turned out to be located at l ~ 60°, b ~ -15°, and cz ~ 2500 km s-1, and the size is about 2500 km s-1 along the direction toward the center.

A search for IRAS galaxies behind the Southern Milky Way

We systematically searched for IRAS galaxies with 60 μm flux density larger than 0.6 Jy by using the UK Schmidt Infrared and IIIa-J Atlases in the Milky Way region (|b| < 15°) between 1 = 210° and 360°. We first selected about 4000 IRAS point sources by using our far-infrared criteria, which are optimized for the search of IRAS galaxies behind the Milky Way region, and then inspected visually the optical counterparts of them on the Schmidt Atlas film copies. We found 966 IRAS sources associated with galaxy-like objects. The list of the objects is presented here with the IRAS source name, Galactic coordinates, IRAS flux densities, field number and emulsion of the Atlas, type and size of galaxy(-like) image, redshift, multiplicity, and cross-identification. Of these, 423 galaxies are already cataloged in the Catalog of Galaxies and Quasars Observed in the IRAS Survey, and most of the remaining 543 galaxy candidates are newly identified in this search