5,545 research outputs found
Early-type Galaxies in the Cluster Abell 2390 at z=0.23
To examine the evolution of the early-type galaxy population in the rich
cluster Abell 2390 at z=0.23 we have gained spectroscopic data of 51 elliptical
and lenticular galaxies with MOSCA at the 3.5 m telescope on Calar Alto
Observatory. This investigation spans both a broad range in luminosity
(-19.3>M_B>-22.3) and uses a wide field of view of 10'x10', therefore the
environmental dependence of different formation scenarios can be analysed in
detail as a function of radius from the cluster centre. Here we present results
on the surface brightness modelling of galaxies where morphological and
structural information is available in the F814W filter aboard the Hubble Space
Telescope (HST) and investigate for this subsample the evolution of the
Fundamental Plane.Comment: 5 pages, 5 figures, to appear in "Carnegie Observatories Astrophysics
Series, Vol. 3: Clusters of Galaxies: Probes of Cosmological Structure and
Galaxy Evolution", ed. J. S. Mulchaey, A. Dressler, and A. Oemler (Pasadena:
Carnegie Observatories,
http://www.ociw.edu/ociw/symposia/series/symposium3/proceedings.html
B3 0003+387: AGN Marked Large-Scale Structure at z=1.47?
We present evidence for a significant overdensity of red galaxies, as much as
a factor of 14 over comparable field samples, in the field of the z=1.47 radio
galaxy B3 0003+387. The colors and luminosities of the brightest red galaxies
are consistent with their being at z>0.8. The radio galaxy and one of the red
galaxies are separated by 5" and show some evidence of a possible interaction.
However, the red galaxies do not show any strong clustering around the radio
galaxy nor around any of the brighter red galaxies. The data suggest that we
are looking at a wall or sheet of galaxies, possibly associated with the radio
galaxy at z=1.47. Spectroscopic redshifts of these red galaxies will be
necessary to confirm this large-scale structure.Comment: 19 pages, 7 figures, LaTeX2e/AASTeX v5.0.2. The full photometric
catalog is included as a separate deluxetable file. To appear in the
Astronomical Journal (~Nov 00
The Environment of Galaxies at Low Redshift
We compare environmental effects in two analogous samples of galaxies, one
from the Sloan Digital Sky Survey (SDSS) and the other from a semi-analytic
model (SAM) based on the Millennium Simulation (MS), to test to what extent
current SAMs of galaxy formation are reproducing environmental effects. We
estimate the large-scale environment of each galaxy using a Bayesian density
estimator based on distances to all ten nearest neighbors and compare
broad-band photometric properties of the two samples as a function of
environment. The feedbacks implemented in the semi-analytic model produce a
qualitatively correct galaxy population with similar environmental dependence
as that seen in SDSS galaxies. In detail, however, the colors of MS galaxies
exhibit an exaggerated dependence on environment: the field contains too many
blue galaxies while clusters contain too many red galaxies, compared to the
SDSS sample. We also find that the MS contains a population of highly
clustered, relatively faint red galaxies with velocity dispersions comparable
to their Hubble flow. Such high-density galaxies, if they exist, would be
overlooked in any low-redshift survey since their membership to a cluster
cannot be determined due to the "Fingers of God" effect.Comment: 15 pages, 5 figures, ApJL accepted, fixed author listing
A Robust Age Indicator for Old Stellar Populations
We derive new spectral H_gamma index definitions which are robust age
indicators for old and relatively old stellar populations and thus have great
potential for solving the age-metallicity degeneracy of galaxy spectra. To
study H_gamma as a function of age, metallicity and resolution, we used a new
spectral synthesis model which predicts SEDs of single-age, single-metallicity
stellar populations at resolution FWHM=1.8A (which can be smoothed to different
resolutions), allowing direct measurements of the equivalent widths of
particular absorption features. We find that the H_gamma strong age
disentangling power strongly depends strongly on the adopted resolution and
galaxy velocity dispersion. We propose a system of indices which are completely
insensitive to metallicity and stable against resolution, allowing the study of
galaxies up to ~300 km/s. Observational spectra of very high S/N and relatively
high dispersion, are required to gain this unprecedented age discriminating
power. Once such spectra are obtained, accurate and reliable estimates for the
luminosity-weighted average stellar ages of these galaxies will become possible
for the first time, without assessing their metallicities. We measured this
index for two globular clusters, a number of low-luminosity elliptical galaxies
and a standard S0 galaxy. We find a large spread in the average stellar ages of
a sample of low-luminosity ellipticals. In particular these indices yield 4 Gyr
for M32, in agreement with the age provided by an extraordinary fit to the full
spectrum of this galaxy that we achieve here.Comment: 22 pages, 4 figures. ApJ, in press. Models and details can be found
at http://www.ioa.s.u-tokyo.ac.jp/~vazdekis
A Richness Study of 14 Distant X-ray Clusters From the 160 Square Degree Survey
We have measured the surface density of galaxies toward 14 X-ray-selected
cluster candidates at redshifts greater than z=0.46, and we show that they are
associated with rich galaxy concentrations. We find that the clusters range
between Abell richness classes 0-2, and have a most probable richness class of
one. We compare the richness distribution of our distant clusters to those for
three samples of nearby clusters with similar X-ray luminosities. We find that
the nearby and distant samples have similar richness distributions, which shows
that clusters have apparently not evolved substantially in richness since
redshift z =0.5. We compare the distribution of distant X-ray clusters in the
L_x--richness plane to the distribution of optically-selected clusters from the
Palomar Distant Cluster Survey. The optically-selected clusters appear overly
rich for their X-ray luminosities when compared to X-ray-selected clusters.
Apparently, X-ray and optical surveys do not necessarily sample identical mass
concentrations at large redshifts. This may indicate the existence of a
population of optically rich clusters with anomalously low X-ray emission. More
likely, however, it reflects the tendency for optical surveys to select
unvirialized mass concentrations, as might be expected when peering along
large-scale filaments.Comment: The abstract has been abridged. Accepted for publication in the
Astrophysical Journa
Damped Lyman alpha Absorbing Galaxies At Low Redshifts z<1 From Hierarchical Galaxy Formation Models
We investigate Damped Ly-alpha absorbing galaxies (DLA galaxies) at low
redshifts z<1 in the hierarchical structure formation scenario to clarify the
nature of DLA galaxies because observational data of such galaxies mainly at
low redshifts are currently available. We find that our model well reproduces
distributions of fundamental properties of DLA galaxies such as luminosities,
column densities, impact parameters obtained by optical and near-infrared
imagings. Our results suggest that DLA systems primarily consist of low
luminosity galaxies with small impact parameters (typical radius about 3 kpc,
surface brightness from 22 to 27 mag arcsec^{-2}) similar to low surface
brightness (LSB) galaxies. In addition, we investigate selection biases arising
from the faintness and from the masking effect which prevents us from
identifying a DLA galaxy hidden or contaminated by a point spread function of a
background quasar. We find that the latter affects the distributions of DLA
properties more seriously rather than the former, and that the observational
data are well reproduced only when taking into account the masking effect. The
missing rate of DLA galaxies by the masking effect attains 60-90 % in the
sample at redshift 0<z<1 when an angular size limit is as small as 1 arcsec.
Furthermore we find a tight correlation between HI mass and cross section of
DLA galaxies, and also find that HI-rich galaxies with M(HI) \sim 10^{9} M_sun
dominate DLA systems. These features are entirely consistent with those from
the Arecibo Dual-Beam Survey which is a blind 21 cm survey. Finally we discuss
star formation rates, and find that they are typically about 10^{-2} M_sun
yr^{-1} as low as those in LSB galaxies.Comment: 21 pages, 13 figures, Accepted for publication in Astrophsical
Journa
Aerosol particles in the Mexican East Pacific <BR> Part I: processing and vertical redistribution by clouds
International audienceAirborne measurements of aerosol particle size distributions were made in the Mexican Intertropical Convergence Zone. The volume concentrations of submicron and super micron particles at cloud base were compared with those in near-cloud regions over a range of altitudes. Of 78 near-cloud regions analyzed, 68% and 45% had enhanced volumes of submicron particles and supermicron particles, respectively. In addition, 35% of these regions had supermicron particles removed, presumably by precipitation. In 61% of the cases the enhancement in volume occurred over the size range from 0.1 to 50 ?m whereas only submicron volumes were enhanced in 35% of the cases. In regions near clouds that were formed in air of maritime origin the frequency of volume enhancement decreased with increasing altitude and was twice as frequent on the dissipating side of clouds compared to the growing side. No such differences were found in the regions near clouds formed in air originating from the land. The frequency and average magnitude of volume enhancement are in qualitative and quantitative agreement with previous observational and theoretical studies that relate enhancements in particle mass to the uptake by cloud droplets of SO2 accompanied by additional growth by droplet coalescence
A backwards approach to the formation of disk galaxies I. Stellar and gas content
A simple chemical enrichment code is described where the two basic mechanisms
driving the evolution of the ages and metallicities of the stellar populations
are the star formation efficiency and the fraction of gas ejected from the
galaxy. Using the observed Tully-Fisher relation in different passbands as a
constraint, it is found that a steep correlation between the maximum disk
rotational velocity and star formation efficiency must exist either for a
linear or a quadratic Schmidt law. Outflows do not play a major role. The
redshift evolution of disk galaxies is explored, showing that a significant
change in the slope of the Tully-Fisher relation is expected because of the
different age distributions of the stellar components in high and low-mass disk
galaxies. The slope measured in the rest frame B,K bands is found to change
from 3(B); 4(K) at z=0 up to 4.5(B); 5(K) at z~1, with a slight dependence on
formation redshift.Comment: Accepted for publication in ApJ. Uses emulateapj.sty. 12 pages with
10 embedded EPS figure
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