293 research outputs found
Observational Test of Environmental Effects on The Local Group Dwarf Spheroidal Galaxies
In this paper, we examine whether tidal forces exerted by the Galaxy or M31
have an influence on the Local Group dwarf spheroidal galaxies (dSphs) which
are their companions. We focus on the surface brightness profiles of the dSphs,
especially their core radii because it is suggested based on the numerical
simulations that tidal disturbance can make core radii extended. We examine the
correlation for the dSphs between the distances from their parent galaxy (the
Galaxy or M31) and the compactnesses of their surface brightness profiles by
using a parameter ``C'' defined newly in this paper. Consequently, we find no
significant correlation. We make some remarks on the origin of this result by
considering three possible scenarios; tidal picture, dark matter picture, and
heterogeneity of the group of dSphs, each of which has been often discussed to
understand fundamental properties and formation processes of dSphs.Comment: 14 pages LaTeX, 2 PostScript figures, to appear in ApJ Letter
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
Constraint on the inflow/outflow rates in star-forming galaxies at z~1.4 from molecular gas observations
We constrain the rate of gas inflow into and outflow from a main-sequence
star-forming galaxy at z~1.4 by fitting a simple analytic model for the
chemical evolution in a galaxy to the observational data of the stellar mass,
metallicity, and molecular gas mass fraction. The molecular gas mass is derived
from CO observations with a metallicity-dependent CO-to-H2 conversion factor,
and the gas metallicity is derived from the H{\alpha} and [NII]{\lambda} 6584
emission line ratio. Using a stacking analysis of CO integrated intensity maps
and the emission lines of H{\alpha} and [NII], the relation between stellar
mass, metallicity, and gas mass fraction is derived. We constrain the inflow
and outflow rates with least-chi-square fitting of a simple analytic chemical
evolution model to the observational data. The best-fit inflow and outflow
rates are ~1.7 and ~0.4 in units of star-formation rate, respectively. The
inflow rate is roughly comparable to the sum of the star-formation rate and
outflow rate, which supports the equilibrium model for galaxy evolution; i.e.,
all inflow gas is consumed by star formation and outflow.Comment: 5 pages, 2 figures, Accepted for publication in the Ap
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