554 research outputs found
Lyman Break Galaxies at z~5: Rest-frame UV Spectra II
We present the results of spectroscopy of Lyman Break Galaxies (LBGs) at z~5
in the J0053+1234 field with the Faint Object Camera and Spectrograph on the
Subaru telescope. Among 5 bright candidates with z' < 25.0 mag, 2 objects are
confirmed to be at z~5 from their Ly alpha emission and the continuum
depression shortward of Ly alpha. The EWs of Ly alpha emission of the 2 LBGs
are not so strong to be detected as Ly alpha emitters, and one of them shows
strong low-ionized interstellar (LIS) metal absorption lines. Two faint objects
with z' \geq 25.0 mag are also confirmed to be at z~5, and their spectra show
strong Ly alpha emission in contrast to the bright ones. These results suggest
a deficiency of strong Ly alpha emission in bright LBGs at z~5, which has been
discussed in our previous paper. Combined with our previous spectra of LBGs at
z~5 obtained around the Hubble Deep Field-North (HDF-N), we made a composite
spectrum of UV luminous (M_1400 \leq -21.5 mag) LBGs at z~5. The resultant
spectrum shows a weak Ly alpha emission and strong LIS absorptions which
suggests that the bright LBGs at z~5 have chemically evolved at least to ~0.1
solar metallicity. For a part of our sample in the HDF-N region, we obtained
near-to-mid infrared data, which constraint stellar masses of these objects.
With the stellar mass and the metallicity estimated from LIS absorptions, the
metallicities of the LBGs at z~5 tend to be lower than those of the galaxies
with the same stellar mass at z \lesssim 2, although the uncertainty is very
large.Comment: 17 pages, 5 figures, accepted for publication in PAS
Discovery of H alpha absorption in the unusual broad absorption line quasar SDSS J083942.11+380526.3
We discovered an H alpha absorption in a broad H alpha emission line of an
unusual broad absorption line quasar, SDSS J083942.11+380526.3 at z=2.318, by
near-infrared spectroscopy with the Cooled Infrared Spectrograph and Camera for
OHS (CISCO) on the Subaru telescope. The Presence of non-stellar H alpha
absorption is known only in the Seyfert galaxy NGC 4151 to date, thus our
discovery is the first case for quasars. The H alpha absorption line is
blueshifted by 520 km/s relative to the H alpha emission line, and its redshift
almost coincides with those of UV low-ionization metal absorption lines. The
width of the H alpha absorption (~ 340 km/s) is similar to those of the UV
low-ionization absorption lines. These facts suggest that the H alpha and the
low-ionization metal absorption lines are produced by the same low-ionization
gas which has a substantial amount of neutral gas. The column density of the
neutral hydrogen is estimated to be ~ 10^18 cm^-2 by assuming a gas temperature
of 10,000 K from the analysis of the curve of growth. The continuum spectrum is
reproduced by a reddened (E(B-V) ~ 0.15 mag for the SMC-like reddening law)
composite quasar spectrum. Furthermore, the UV spectrum of SDSS
J083942.11+380526.3 shows a remarkable similarity to that of NGC 4151 in its
low state, suggesting the physical condition of the absorber in SDSS
J083942.11+380526.3 is similar to that of NGC 4151 in the low state. As
proposed for NGC 4151, SDSS J083942.11+380526.3 may be also seen through the
close direction of the surface of the obscuring torus.Comment: Accepted for publication in Ap
Lyman Break Galaxies at : Rest-Frame UV Spectra
We report initial results for spectroscopic observations of candidates of
Lyman Break Galaxies (LBGs) at in a region centered on the Hubble Deep
Field-North by using the Faint Object Camera and Spectrograph attached to the
Subaru Telescope. Eight objects with mag, including one AGN, are
confirmed to be at . The rest-frame UV spectra of seven LBGs
commonly show no or weak Lyalpha emission line (rest-frame equivalent width of
0-10\AA) and relatively strong low-ionization interstellar metal absorption
lines of SiII 1260, OI+SiII 1303, and CII 1334 (mean
rest-frame equivalent widths of them are \AA). These
properties are significantly different from those of the mean rest-frame UV
spectrum of LBGs at , but are quite similar to those of subgroups of
LBGs at with no or weak Lyalpha emission. The weakness of Lyalpha
emission and strong low-ionization interstellar metal absorption lines may
indicate that these LBGs at are chemically evolved to some degree and
have a dusty environment. Since the fraction of such LBGs at in our
sample is larger than that at , we may witness some sign of evolution
of LBGs from to , though the present sample size is very
small. It is also possible, however, that the brighter LBGs tend to show no or
weak Lyalpha emission, because our spectroscopic sample is bright (brighter
than ) among LBGs at . More observations are required to
establish spectroscopic nature of LBGs at .Comment: 16 pages, 3 figures, accepted by Ap
Activation Analysis of Lanthanum and Europium in Sea Water and Lake Water (Physical and Inorganic Chemistry)
Transition of the Stellar Initial Mass Function Explored with Binary Population Synthesis
The stellar initial mass function (IMF) plays a crucial role in determining
the number of surviving stars in galaxies, the chemical composition of the
interstellar medium, and the distribution of light in galaxies. A key unsolved
question is whether the IMF is universal in time and space. Here we use
state-of-the-art results of stellar evolution to show that the IMF of our
Galaxy made a transition from an IMF dominated by massive stars to the
present-day IMF at an early phase of the Galaxy formation. Updated results from
stellar evolution in a wide range of metallicities have been implemented in a
binary population synthesis code, and compared with the observations of
carbon-enhanced metal-poor (CEMP) stars in our Galaxy. We find that applying
the present-day IMF to Galactic halo stars causes serious contradictions with
four observable quantities connected with the evolution of AGB stars.
Furthermore, a comparison between our calculations and the observations of CEMP
stars may help us to constrain the transition metallicity for the IMF which we
tentatively set at [Fe/H] = -2. A novelty of the current study is the inclusion
of mass loss suppression in intermediate-mass AGB stars at low-metallicity.
This significantly reduces the overproduction of nitrogen-enhanced stars that
was a major problem in using the high-mass star dominated IMF in previous
studies. Our results also demonstrate that the use of the present day IMF for
all time in chemical evolution models results in the overproduction of Type I.5
supernovae. More data on stellar abundances will help to understand how the IMF
has changed and what caused such a transition.Comment: 8 pages, 2 figures, accepted by MNRAS Lette
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