Toshinori Maihara

Diffuse Extragalactic Background Light versus Deep Galaxy Counts in the Subaru Deep Field: Missing Light in the Universe?*

Deep optical and near-infrared galaxy counts are utilized to estimate the extragalactic background light (EBL) coming from normal galactic light in the universe. Although the slope of the number-magnitude relation of the faintest counts is flat enough for the count integration to converge, a considerable fraction of EBL from galaxies could still have been missed in deep galaxy surveys because of various selection effects, including the cosmological dimming of the surface brightness of galaxies. Here we give an estimate of EBL from galaxy counts, in which these selection effects are quantitatively taken into account for the first time, based on reasonable models of galaxy evolution that are consistent with all available data of galaxy counts, size, and redshift distributions. We show that the EBL from galaxies is best resolved into discrete galaxies in the near-infrared bands (J, K) by using the latest data of the Subaru Deep Field; more than 80%-90% of EBL from galaxies has been resolved in these bands. Our result indicates that the contribution by missing galaxies cannot account for the discrepancy between the count integration and recent tentative detections of diffuse EBL in the K band (2.2 μm), and there may be a very diffuse component of EBL that has left no imprints in known galaxy populations.

Near-Infrared Faint Galaxies in the Subaru Deep Field: Comparing the Theory with Observations for Galaxy Counts, Colors, and Size Distributions to K ~ 24.5*

Galaxy counts in the K band, (J-K) colors, and apparent size distributions of faint galaxies in the Subaru Deep Field (SDF) down to K ~ 24.5 were studied in detail. Special attention has been paid to take into account various selection effects, including the cosmological dimming of surface brightness, to avoid any systematic bias that may be the origin of controversy in previously published results. We also tried to be very careful about systematic model uncertainties; we present a comprehensive survey of these systematic uncertainties and dependence on various parameters, and we have shown that the dominant factors to determine galaxy counts in this band are cosmology and number evolution. We found that the pure luminosity evolution (PLE) model is very consistent with all the SDF data down to K ~ 22.5, without any evidence for number or size evolution in a low-density, ?-dominated flat universe, which is now favored by various cosmological observations. On the other hand, a number evolution of galaxies with ? ~ 2, when invoked as the luminosity conserving mergers as * (1 + z)? and L* (1 + z)-? for all types of galaxies, is necessary to explain the data in the Einstein-de Sitter universe. If the popular ?-dominated universe is taken for granted, our result then gives a strong constraint on the number evolution of giant elliptical or early-type galaxies to z ~ 1-2 that must be met by any models in the hierarchically clustering universe, since such galaxies are the dominant population in this magnitude range (K 22.5). A number evolution with ? ~ 1 is already difficult to reconcile with the data in this universe. On the other hand, number evolution of late-type galaxies and/or dwarf galaxies, which has been suggested by previous studies of optical galaxies, is allowed from the data. In the fainter magnitude range of K 22.5, we found a slight excess of observed counts over the prediction of the PLE model when elliptical galaxies are treated as a single population. We suggest that this discrepancy reflects some number evolution of dwarf galaxies and/or the distinct populations of giant and dwarf elliptical galaxies which have been known for local elliptical galaxies.

NIR Spectroscopy of Star-Forming Galaxies at z ∼ 1.4 with Subaru/FMOS: The Mass–Metallicity Relation

We present near-infrared spectroscopic observations of star-forming galaxies at z � 1.4 with FMOS on the Subaru Telescope. We observed K-band selected galaxies in the SXDS/UDS fields with K � 23.9mag, 1.2 � zph � 1.6, M� � 10 9:5 Mˇ, andexpectedF(H˛) � 10 � 16 ergs � 1 cm � 2 ; 71objectsin the sample havesignificantdetections of H˛. For these objects, excluding possible AGNs, identified from the BPT diagram, gas-phase metallicities were obtained from the [NII]/H˛ line ratio. The sample is split into three stellar-mass bins, and the spectra are stacked in each stellar-mass bin. The mass‐metallicity relation obtained at z � 1.4 is located between those at z � 0.8 and z � 2.2. We constrain the intrinsic scatter to be � 0.1dex, or larger in the mass‐metallicity relation at z � 1.4; the scatter may be larger at higher redshifts. We found trends that the deviation from the mass‐metallicity relation depends on the SFR (Star-formation rate) and the half light radius: Galaxies with higher SFR and larger half light radii show lower metallicities at a given stellar mass. One possible scenario for the trends is the infall of pristine gas accreted from IGM, or through merger events. Our data points show larger scatter than the fundamental metallicity relation (FMR) at z � 0.1, and the averagemetallicities slightly deviate fromthe FMR. The compilationof the mass‐ metallicity relations at z � 3t oz � 0.1 shows that they evolve smoothly from z � 3t oz � 0 without changing the shape so much, except for the massive part at z � 0.

OBSERVATIONS OF THE OH AIRGLOW EMISSION

The OH airglow emission in the J- and H-bands was observed for the purpose of determining the line widths, the precise wavelengths of individual lines, and also the continuum emission level between lines. The lines were not resolved with a resolving power of about 17000. Wavelengths and intensities were measured for approximately 120 lines from 1.1 to 1.8 microns. The continuum emission intensity was also measured on a dark night and was as low as 590 photons s-1m-2 arcsec-2 um-1 at 1.665 um. The level is about one fiftieth the average of the OH airglow emission in the H-band.

Morphologies and Color Gradients of Luminous Evolved Galaxies at z ~ 1.5*

We have examined in detail the morphologies of seven -->z ~ 1.5 passively evolving luminous red galaxies using high-resolution HST NICMOS and ACS imaging data. Almost all of these galaxies appear to be relaxed systems, with smooth morphologies at both rest-frame UV and visible wavelengths. Previous results from spectral synthesis modeling favor a single burst of star formation more than 1 Gyr before the observed epoch. The prevalence of old stellar populations, however, does not correlate exclusively with early-type morphologies as it does in the local universe; the light profiles for some of these galaxies appear to be dominated by massive exponential disks. This evidence for massive old disks, along with the apparent uniformity of stellar age across the disk, suggests formation by a mechanism better described as a form of monolithic collapse than as a hierarchical merger. These galaxies could not have undergone a single major merging event since the bulk of their stars were formed, more than 1 Gyr earlier. There is at least one case, however, that appears to be undergoing a dry merger, which may be an example of the process that converts these unusual galaxies into the familiar spheroids that dominate galaxies comprising old stellar populations at the present epoch.

Subaru Deep Survey I. Near-Infrared Observations

Deep near-infraredimages of a blank 2 � ×2 � section of skynear the galactic north pole taken by Subaru Telescope are presented. The total integration times of the J and Kbands were 12.1 hr and 9.7 hr, resulting in 5 σ limiting magnitudes of 25.1 and 23.5 mag, respectively. The numbers of sources within these limiting magnitudes found with an automated detection procedure are 385 in the J band and 350 in K � . Based on photometric measurements of these sources, we present number count vs. magnitude relations, color vs. magnitude diagrams, size vs. color relationships, etc. The slope of the galaxy number count plotted against the AB magnitude scale is about 0.23 in the 22 to 26 AB magnitude range of both bands. The spatial number density of galaxies as well as the slopes in the faint-end region given by the Subaru Deep Field (SDF) survey are consistent with those given by HST-NICMOS surveys, as expressed on the AB magnitude diagram. Several sources having very large J − Kcolor have been found, including a few Kobjects without detection at J. In addition, a number of faint galactic stars were also

The mass-metallicity relation at z 1.4 revealed with Subaru/FMOS

We present a stellar mass-metallicity relation at z ~ 1.4 with an unprecedentedly large sample of ~340 star-forming galaxies obtained with FibreMulti-Object Spectrograph (FMOS) on the Subaru Telescope. We observed K-band selected galaxies at 1.2 ≤ zph ≤ 1.6 in the Subaru XMM-Newton Deep Survey/Ultra Deep Survey fields with M*> 109.5M⊙, and expected F(Hα) > 5 × 10-17 erg s-1 cm-2. Among the observed ~1200 targets, 343 objects show significant Ha emission lines. The gas-phase metallicity is obtained from [N II] λ6584/Hα line ratio, after excluding possible active galactic nuclei. Due to the faintness of the [N II] λ6584 lines, we apply the stacking analysis and derive the mass-metallicity relation at z ~ 1.4. Our results are compared to past results at different redshifts in the literature. The mass-metallicity relation at z ~ 1.4 is located between those at z ~ 0.8 and z ~ 2.2; it is found that the metallicity increases with decreasing redshift from z ~ 3 to z ~ 0 at fixed stellar mass. Thanks to the large size of the sample, we can study the dependence of the mass-metallicity relation on various galaxy physical properties. The average metallicity from the stacked spectra is close to the local Fundamental Metallicity Relation (FMR) in the higher metallicity part but >0.1 dex higher in metallicity than the FMR in the lower metallicity part.We find that galaxies with larger E(B -V), B -R and R -H colours tend to show higher metallicity by ~0.05 dex at fixed stellar mass. We also find relatively clearer size dependence that objects with smaller half-light radius tend to show higher metallicity by ~0.1 dex at fixed stellar mass, especially in the low-mass part.

Fe II/Mg II Emission-Line Ratios of QSOs. II. z > 6 Objects

Near-infrared spectra of four QSOs located at

A Disk Galaxy of Old Stars at z ~ 2.5*

z>6

Fe II/Mg II Emission-Line Ratios of QSOs within 0 < z < 5.3

are obtained with the OH-airglow suppressor mounted on the Subaru telescope. The FeII/MgII emission-line ratios of these QSOs are examined by the same fitting algorithm as in our previous study of