201 research outputs found
Exploring Galaxy Evolution from Infrared Number Counts and Cosmic Infrared Background
Recently reported infrared (IR) galaxy number counts and cosmic infrared
background (CIRB) all suggest that galaxies have experienced a strong evolution
sometime in their lifetime. We statistically estimate the galaxy evolution
history from these data. We find that an order of magnitude increase of the
far-infrared (FIR) luminosity at redshift z = 0.5 - 1.0 is necessary to
reproduce the very high CIRB intensity at 140 um reported by Hauser et al.
(1998). z \sim 0.75 and decreases to, even at most, a factor of 10 toward z
\sim 5, though many variants are allowed within these constraints. This
evolution history also satisfies the constraints from the galaxy number counts
obtained by IRAS, ISO and, roughly, SCUBA. The rapid evolution of the comoving
IR luminosity density required from the CIRB well reproduces the very steep
slope of galaxy number counts obtained by ISO. We also estimate the cosmic star
formation history (SFH) from the obtained FIR luminosity density, considering
the effect of the metal enrichment in galaxies. The derived SFH increases
steeply with redshift in 0
0.75. This is consistent with the SFH estimated from the reported ultraviolet
luminosity density. In addition, we present the performance of the Japanese
ASTRO-F FIR galaxy survey. We show the expected number counts in the survey. We
also evaluate how large a sky area is necessary to derive a secure information
of galaxy evolution up to z \sim 1 from the survey, and find that at least 50 -
300 deg^2 is required.Comment: 18 pages LaTeX, PASJ in press. Abstract abridge
Age Dating of a High-Redshift QSO B1422+231 at Z=3.62 and its Cosmological Implications
The observed Fe II(UV+optical)/Mg II lambda lambda 2796,2804 flux ratio from
a gravitationally lensed quasar B1422+231 at z=3.62 is interpreted in terms of
detailed modeling of photoionization and chemical enrichment in the broad-line
region (BLR) of the host galaxy. The delayed iron enrichment by Type Ia
supernovae is used as a cosmic clock. Our standard model, which matches the Fe
II/Mg II ratio, requires the age of 1.5 Gyr for B1422+231 with a lower bound of
1.3 Gyr, which exceeds the expansion age of the Einstein-de Sitter Omega_0=1
universe at a redshift of 3.62 for any value of the Hubble constant in the
currently accepted range, H_0=60-80 km,s^{-1},Mpc^{-1}. This problem of an age
discrepancy at z=3.62 can be unraveled in a low-density Omega_0<0.2 universe,
either with or without a cosmological constant, depending on the allowable
redshift range of galaxy formation. However, whether the cosmological constant
is a required option in modern cosmology awaits a thorough understanding of
line transfer processes in the BLRs.Comment: 7 pages including 3 figures, to appear in ApJ Letter
Supernova dust for the extinction law in a young infrared galaxy at z = 1
We apply the supernova(SN) extinction curves to reproduce the observed
properties of SST J1604+4304 which is a young infrared (IR) galaxy at z = 1.
The SN extinction curves used in this work were obtained from models of unmixed
ejecta of type II supernovae(SNe II) for the Salpeter initial mass function
(IMF) with a mass range from 8 to 30 M_sun or 8 to 40 M_sun.
The effect of dust distributions on the attenuation of starlight is
investigated by performing the chi-square fitting method against various dust
distributions. These are the commonly used uniform dust screen, the clumpy dust
screen, and the internal dust geometry. We add to these geometries three
scattering properties, namely, no-scattering, isotropic scattering, and
forward-only scattering. Judging from the chi-square values, we find that the
uniform screen models with any scattering property provide good approximations
to the real dust geometry. Internal dust is inefficient to attenuate starlight
and thus cannot be the dominant source of the extinction.
We show that the SN extinction curves reproduce the data of SST J1604+4304
comparable to or better than the Calzetti extinction curve. The Milky Way
extinction curve is not in satisfactory agreement with the data unless several
dusty clumps are in the line of sight. This trend may be explained by the
abundance of SN-origin dust in these galaxies; SN dust is the most abundant in
the young IR galaxy at z = 1, abundant in local starbursts, and less abundant
in the Galaxy. If dust in SST J1604+4304 is dominated by SN dust, the dust
production rate is about 0.1 M_sun per SN.Comment: 12 pages, 8 figures, 1 tabl
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