39 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
Deficit of Far-Infrared [CII] Line Emission toward the Galactic Center
We have observed the [CII] 158 micron line emission from the Galactic plane
(-10 deg < l < 25 deg, |b| <= 3 deg) with the Balloon-borne Infrared Carbon
Explorer (BICE). The observed longitudinal distribution of the [CII] line
emission is clearly different from that of the far-infrared continuum emission;
the Galactic center is not the dominant peak in the [CII] emission. Indeed, the
ratio of the [CII] line emission to far-infrared continuum (I_[CII] / I_FIR) is
systematically low within the central several hundred parsecs of the Galaxy.
The observational results indicate that the abundance of the C+ ions themselves
is low in the Galactic center. We attribute this low abundance mainly to soft
UV radiation with fewer C-ionizing photons. This soft radiation field, together
with the pervasively high molecular gas density, makes the molecular
self-shielding more effective in the Galactic center. The self-shielding
further reduces the abundance of C+ ions, and raises the temperature of
molecular gas at the C+/C/CO transition zone.Comment: Compressed uuencoded postcript, 15 pages with 2 figures, to appear in
the Astrophysical Journal (Letters
Faint 6.7um Galaxies and their Contributions to the Stellar Mass Density in the Universe
We discuss the nature of faint 6.7um galaxies detected with the mid-infrared
camera ISOCAM on board the Infrared Space Observatory (ISO). The 23 hour
integration on the Hawaii Deep Field SSA13 has provided a sample of 65 sources
down to 6uJy at 6.7um. For 57 sources, optical or near-infrared counterparts
were found with a statistical method. All four Chandra sources, three SCUBA
sources, and one VLA/FIRST source in this field were detected at 6.7um with
high significance. Using their optical to mid-infrared colors, we divided the
6.7um sample into three categories: low redshift galaxies with past histories
of rapid star formation, high redshift ancestors of these, and other star
forming galaxies. Rapidly star forming systems at high redshifts dominate the
faintest end. Spectroscopically calibrated photometric redshifts were derived
from fits to a limited set of template SEDs. They show a high redshift tail in
their distribution with faint (1. The 6.7um galaxies tend
to have brighter K magnitudes and redder I-K colors than the blue dwarf
population at intermediate redshifts. Stellar masses of the 6.7um galaxies were
estimated from their rest-frame near-infrared luminosities. Massive galaxies
(M_star~10e11M_sun) were found in the redshift range of z=0.2-3. Epoch
dependent stellar mass functions indicate a decline of massive galaxies'
comoving space densities with redshift. Even with such a decrease, the
contributions of the 6.7um galaxies to the stellar mass density in the universe
are found to be comparable to those expected from UV bright galaxies detected
in deep optical surveys.Comment: 31 pages, 15 figures, AJ (accepted), a version with color figures at
http://www.ioa.s.u-tokyo.ac.jp/~ysato/pub/3/p3c-ysato.ps.g
The Far-Infrared Surveyor (FIS) for AKARI
The Far-Infrared Surveyor (FIS) is one of two focal plane instruments on the
AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 um, and
uses two kinds of array detectors. The FIS arrays and optics are designed to
sweep the sky with high spatial resolution and redundancy. The actual scan
width is more than eight arcmin, and the pixel pitch is matches the diffraction
limit of the telescope. Derived point spread functions (PSFs) from observations
of asteroids are similar to the optical model. Significant excesses, however,
are clearly seen around tails of the PSFs, whose contributions are about 30% of
the total power. All FIS functions are operating well in orbit, and its
performance meets the laboratory characterizations, except for the two longer
wavelength bands, which are not performing as well as characterized.
Furthermore, the FIS has a spectroscopic capability using a Fourier transform
spectrometer (FTS). Because the FTS takes advantage of the optics and detectors
of the photometer, it can simultaneously make a spectral map. This paper
summarizes the in-flight technical and operational performance of the FIS.Comment: 23 pages, 10 figures, and 2 tables. Accepted for publication in the
AKARI special issue of the Publications of the Astronomical Society of Japa
Hepatitis C virus infection among maintenance hemodialysis patients: A preventable problem of the world
Hepatitis C virus (HCV) infection, unrelated to blood transfusion is very common among hemodialysis patients with chronic renal failure. The positivity rate for anti-HCV varies from 18% to 91% among various countries. It is due not only to the past blood transfusions, but also to nosocomial transmission which is preventable. The main route of virus entry, is most likely, the two (arterial and venous) needle holes that are touched by the fingers of the physi-cian and the nurse repeatedly. The recommended preventive measures include: the use of a sterile glove, finger sterilization with a disinfectant solution, immediately before touching the needle/needle hole. and repeated education of the staff. Whether the anti-HCV positive patients should be separated from the negative, largely depends on the prevalence of HCV infection within the dialysis unit