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 number-magnitude relation of the faintest counts is flat enough for the count integration to converge, 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 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 which 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 micron), and there may be a very diffuse component of EBL which has left no imprints in known galaxy populations.Comment: ApJ Letters in press. Two new reports on the diffuse EBL at 1.25 and 2.2 microns are added to the reference list and Table

FeII/MgII Emission Line Ratios of QSOs. II. z>6 Objects

Near-infrared spectra of four QSOs located at $z>6$ 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 $z<5.3$ QSOs. The fitting results show that two out of the four $z>6$ QSOs have significant FeII emission in their rest-UV spectra, while the other two have almost no FeII features. We also applied our fitting algorithm to more than 10,000 SDSS QSOs and found two trends in the distribution of FeII/MgII against redshift: (1) the upper envelope of the FeII/MgII distribution at $z>3$ shows a probable declination toward high redshift, and (2) the median distribution settles into lower ratios at $z\sim 1.5$ with small scatter compared to the other redshift. We discuss an Fe/Mg abundance evolution of QSOs with a substantial contribution from the diverse nature of the broad-line regions in high-redshift QSOs.Comment: 12 pages, 2 figures. Accepted for publication in ApJ (10 October 2004, v614

Near-Infrared Spectroscopy of the Cool Brown Dwarf, SDSS 1624+00

Using the Subaru Telescope, we have obtained multiple near-infrared spectra of the cool brown dwarf, SDSS 1624+00, in search of spectral variability in an 80 minute time span. We have found the suspected variability of water vapor absorption throughout the observations, which requires confirmation by a longer time baseline. After coadding the spectra, we have obtained a high-quality spectrum covering 1.05 to 1.8 um. Three kinds of spectral indicators, the water vapor bands, methane band, and KI lines in J band, suggest that SDSS 1624+00 is warmer and dustier than Gl 229B.Comment: 6 figures, to appear in PAS

Infrared Imaging of z=2.43 Radio Galaxy B3 0731+438 with the Subaru Telescope - Detection of Hα\alpha Ionization Cones of a Powerful Radio Galaxy

We report on infrared imaging observations of the z=2.429 radio galaxy B3 0731+438 with the Subaru telescope. The images were taken with the K'-band filter and the 2.25 um narrow-band filter to examine the structure and properties of the Ha+[N II] 6548,6583 emission-line components. The Ha+[N II] emission-line image shows biconical lobes with an extent of 40 kpc, which are aligned with the radio axis. The rest-frame equivalent widths of the emission lines at these cones are as large as 1100 AA, and can be well explained by a gas-cloud model photoionized by power-law continuum radiation. The isotropic ionizing photon luminosity necessary to ionize the hydrogen gas in these cones amounts to 1e57(photons/s), which is larger than that in the majority of radio-loud QSOs. From these results, we propose that the Ha alignment effect in this object is produced by biconical gas clouds, which are swept up by the passage of radio jets, and are ionized by strong UV radiation from a hidden AGN. The continuum image consists of two components, a stellar-like point source and an extended diffuse galaxy. These are supposed to be a type-2 AGN and its host galaxy. The SED is fitted by a combination of spectra of a reddened dust-scattered AGN and an instantaneous starburst population of 500 Myr old. The stellar mass of the galaxy is estimated to be 3e11 M_solar, which is as large as that of typical 3C radio galaxies at z=1.Comment: 12 pages, 4 Postscript figures, uses PASJ2.sty, PASJ95.sty, PASJadd.sty. Accepted for publication in PASJ (2000

Nature of a Strongly-Lensed Submillimeter Galaxy SMM J14011+0252

We have carried out near-infrared JHK spectroscopy of a gravitationally lensed submillimeter galaxy SMM J14011+0252 at z=2.565, using OHS and CISCO on the Subaru telescope. This object consists of two optical components, J1 and J2, which are lensed by the cluster Abell 1835. J1 suffers additional strong lensing by a foreground galaxy at z=0.25 in the cluster. The rest-optical H-alpha, H-beta, and [O II]3727 lines are detected in both J1 and J2, and [N II]6548,6583 lines are also detected in J1. A diagnosis of emission-line ratios shows that the excitation source of J1 is stellar origin, consistent with previous X-ray observations. The continua of J1 and J2 show breaks at rest 4000A, indicating relatively young age. Combined with optical photometry, we have carried out model spectrum fitting of J2 and find that it is a very young (~50 Myr) galaxy of rather small mass (~10e8 M_sol) which suffers some amount of dust extinction. A new gravitational lensing model is constructed to assess both magnification factor and contamination from the lensing galaxy of the component J1, using HST-F702W image. We have found that J1 suffers strong lensing with magnification of ~30, and its stellar mass is estimated to be < 10e9 M_sol. These results suggest that SMM J14011+0252 is a major merger system at high redshift that undergoes intense star formation, but not a formation site of a giant elliptical. Still having plenty of gas, it will transform most of the gas into stars and will evolve into a galaxy of < 10e10 M_sol. Therefore, this system is possibly an ancestor of a less massive galaxy such as a mid-sized elliptical or a spiral at the present.Comment: 21 pages, 11 figures. Accepted for publication in Astronomical Journa

A Disk Galaxy of Old Stars at z ~ 2.5

We describe observations of a galaxy in the field of the $z=2.483$ radio galaxy 4C 23.56, photometrically selected to have a spectral-energy distribution consistent with an old stellar population at the redshift of the radio galaxy. Exploration of redshift--stellar-population-reddening constraints from the photometry indicates that the galaxy is indeed at a redshift close to that of 4C23.56, that the age of the most recent significant star formation is roughly >~2 Gyr, and that reddening is fairly modest, with more reddening required for the younger end of stellar age range. From analysis of a deep adaptive-optics image of the galaxy, we find that an r^1/4-law profile, common for local spheroidal galaxies, can be excluded quite strongly. On the other hand, a pure exponential profile fits remarkably well, while the best fit is given by a Sersic profile with index n=1.49. Reconstruction of the two-dimensional form of the galaxy from the best-fit model is consistent with a disk galaxy with neither a significant bulge component nor gross azimuthal structure. The assembly of roughly 2L* of old stars into such a configuration this early in the history of the universe is not easily explainable by any of the currently popular scenarios for galaxy formation. A galaxy with these properties would seem to require smooth but rapid infall of the large mass of gas involved, followed by a burst of extremely vigorous and efficient star formation in the resulting disk.Comment: 8 pages, 6 figures, emulateapj.sty, accepted for publication in The Astrophysical Journa