643 research outputs found
Optical (VRI) Photometry in the Field of the Galaxy Cluster AC 118 at z=0.31
We present new photometric V-, R- and I-band data for the rich galaxy cluster
AC 118 at z=0.31. The new photometry covers an area of 8.6x8.6 arcmin,
corresponding to 2.92.9 Mpc (H km s Mpc,
q and ). The data have been collected for a project aimed
at studying galaxy evolution through the color-magnitude relation and the
fundamental plane. We provide a catalogue including all the sources (N = 1206)
detected in the cluster field. The galaxy sample is complete to V=22.8 mag
(N_gal=574), R=22.3 mag (N_gal=649) and I=20.8 mag (N_gal=419). We give
aperture magnitudes within a fixed aperture of 4.4 arcsec and Kron magnitudes.
We also give photometric redshifts for 459 sources for which additional U- and
K-band photometry is available. We derive and discuss the V- and R-band
luminosity functions. The catalogue, which is distributed in electronic form,
is intended as a tool for studies in galaxy evolution.Comment: 15 pages, 6 figures, A&A in pres
Photometric Properties of Galaxy Population in the Cluster EIS 0048-2942 at z~0.64
~Deep photometric data in the V-, R-, I-, z- and K-bands for the cluster of
galaxies EIS 0048-2942 are used to investigate the properties of the galaxy
populations at z~0.64 in a field of 2.5x2.5 Mpc^2. The sample of candidate
cluster members (N = 171) is selected by the photometric redshift technique and
is complete up to I=22.5. Galaxies were classified as spheroids and disks
according to the shape of the light profile in the I-band, as parametrized by
the Sersic index. In both optical and NIR, spheroids define a sharp
colour-magnitude sequence, whose slope and zero points are consistent with a
high formation redshift (z_f > 2). The disk population occupies a different
region in the colour-magnitude diagram, having bluer colours with respect to
the red sequence. Interestingly, we find some level of mixing between the
properties of the two classes: some disks lie on the colour-magnitude sequence
or are redder, while some spheroids turn out to be bluer. The spatial
distribution of cluster galaxies show a clumpy structure, with a main
over-density of radius ~0.5 Mpc, and at least two other clumps distant ~1 Mpc
from the center. The various sub-structures are mostly populated by the red
galaxies, while the blue population has an almost uniform distribution. The
fraction of blue galaxies in EIS 0048-2942 is f_B=0.11 +/-0.07. This is much
lower than what expected on the basis of the Butcher-Oemler effect at lower
redshifts.Comment: 22 pages, 12 figures. A&A in pres
Age, Metallicity and Star Formation History of Cluster Galaxies at z~0.3 F
We investigate the color-magnitude distribution in the rich cluster AC 118 at
z=0.31. The sample is selected by the photometric redshift technique, allowing
to study a wide range of properties of stellar populations, and is complete in
the K-band, allowing to study these properties up to a given galaxy mass. We
use galaxy templates based on population synthesis models to translate the
physical properties of the stellar populations - formation epoch, time-scale of
star formation, and metallicity - into observed magnitudes and colors. In this
way we show that a sharp luminosity-metallicity relation is inferred without
any assumption on the galaxy formation scenario (either monolithic or
hierarchical). Our data exclude significant differences in star formation
histories along the color-magnitude relation, and therefore confirm a pure
metallicity interpretation for its origin, with an early (z~5) formation epoch
for the bulk of stellar populations. The dispersion in the color-magnitude
diagram implies that fainter galaxies in our sample (K~18) ceased to form stars
as late as z~0.5, in agreement with the picture that these galaxies were
recently accreted into the cluster environment. The trend with redshift of the
total stellar mass shows that half of the luminous mass in AC 118 was already
formed at $z~2, but also that 20% of the stars formed at z<1.Comment: 16 pages, 10 figures. ApJ in pres
The Fundamental Planes of E+A galaxies and GALEX UV-excess early-type galaxies: Revealing their intimate connection
Strong Balmer absorption lines and the lack of Ha and [OII] emission lines
signify that E+As are post-starburst systems. Recent studies suggest that E+As
may undergo the transition from the `blue cloud' to the `red sequence' and
eventually migrate to red sequence ETGs. An observational validation of this
scenario is to identify the intervening galaxy population between E+As and the
red-sequence. Motivated by recent findings with GALEX that a large fraction of
ETGs exhibit UV-excess as a sign of RSF, we investigate the possible connection
of the UV-excess galaxies to E+As. In particular, we examine the FP scaling
relations of the largest sample of ~1,000 E+As selected from the SDSS and
~20,000 morphologically-selected SDSS ETGs with GALEX UV data. The FP
parameters, combined with stellar population indicators, reveal a certain group
of UV-excess ETGs that bridges between E+As and quiescent red galaxies. The
newly identified galaxies are the post-starburst systems characterized by
UV-excess but no Ha emission. This is a conceptual generalisation of "E+A", in
that the Balmer absorption line in the "E+A" definition is replaced with
UV-optical colours that are far more sensitive to RSF than the Balmer lines. We
refer to these UV-excess galaxies as "E+a" galaxies, which stands for
elliptical ("E") galaxies with a minority of A-type ("a") young stars. The
species are either (1) galaxies that experienced starbursts weaker than those
observed in E+As (1~10% of E+As, "mild E+As") or (2) the products of passively
evolved E+As after quenching star formation quite a while ago (~1 Gyr, "old
E+As"). We suggest that the latter type of E+a galaxies represents the most
recent arrival to the red sequence in the final phase of the "E+A" to "red
early-type" transition. (Abridged)Comment: 15 pages, 15 figures, Accepted for publication in MNRA
An H-alpha survey of the rich cluster A1689
(Abridged) We present results of an H-alpha survey in the rich cluster A1689
at z=0.18, using the LDSS++ spectrograph on the AAT. We obtained spectra
covering redshifted H-alpha for 522 galaxies brighter than I=22.5, covering a
field of 8.7'X8.7'. We detect H-alpha emission in 46 of these galaxies;
accounting for selection effects due to sampling and cluster membership, we
determine that 24% of cluster members brighter than M_R=-16.5+5log(h) are
detected with H-alpha flux greater than 4h^{-2}X 10^{38} ergs/s. This
corresponds to a limiting star formation rate of 0.008 h^{-2} Msun/yr, assuming
1 magnitude of dust extinction. From a Hubble Space Telescope mosaic covering
7.5' X 10.0', we determine morphologies for 199 galaxies brighter than I=21,
and find that 20% of the cluster members are of type Sa or later. More than 90%
of cluster spirals show H-alpha emission, compared with less than 10% of E and
S0 galaxies. The cluster H-alpha luminosity function has a low normalisation
relative to the z~0.2 field, by ~50%, after accounting for the different
fraction of spiral galaxies in the two environments. When compared with local
field galaxies, this suggests that star formation activity is suppressed in
early-type cluster galaxies, relative to their field counterparts. Our sample
includes 29 galaxies previously observed with ISOCAM at 6 and 15 microns. We
detect all 15-micron sources at H-alpha, so there is no evidence for any star
formation completely hidden at H-alpha. Comparing the 15-micron and H-alpha
fluxes, we find evidence that some mid-infrared-detected galaxies could be
obscured by as much as 3 magnitudes of extinction at H-alpha, although this
depends on the largely unknown contribution from any AGN-heated dust to the
mid-infrared flux.Comment: MNRAS - resubmitted after referee report, March 1
The nature of the SDSS galaxies in various classes based on morphology, colour and spectral features -- I. Optical properties
We present a comprehensive study of the nature of the SDSS galaxies divided
into various classes based on their morphology, colour, and spectral features.
The SDSS galaxies are classified into early-type and late-type; red and blue;
passive, HII, Seyfert, and LINER, returning a total of 16 fine classes of
galaxies. We examine the luminosity dependence of seven physical parameters of
galaxies in each class. We find that more than half of red early-type galaxies
(REGs) have star formation or AGN activity, and that these active REGs have
smaller axis ratio and bluer outside compared to the passive REGs. Blue
early-type galaxies (BEGs) show structural features similar to those of REGs,
but their centres are bluer than REGs. HII BEGs are found to have bluer centres
than passive BEGs, but HII REGs have bluer outside than passive REGs.
Bulge-dominated late-type galaxies have red colours. Passive red late-types are
similar to REGs in several aspects. Most blue late-type galaxies (BLGs) have
forming stars, but a small fraction of BLGs do not show evidence for current
star formation activity. Differences of other physical parameters among
different classes are inspected, and their implication on galaxy evolution is
discussed.Comment: 16 pages, 10 tables, 16 figures; accepted for publication in MNRA
Young ages and other intriguing properties of massive compact galaxies in the Local Universe
We characterize the kinematics, morphology, stellar populations and star
formation histories of a sample of massive compact galaxies in the nearby
Universe, which might provide a closer look to the nature of their high
redshift (z > 1.0) massive counterparts. We find that nearby compact massive
objects show elongated morphologies and are fast rotators. New high-quality
long-slit spectra show that they have young mean luminosity-weighted ages (<
2Gyr) and solar metallicities or above ([Z/H]> 0.0). No significant stellar
population gradients are found. The analysis of their star formation histories
suggests that these objects have experienced recently enormous bursts which, in
some cases, represent unprecedented large fractions of their total stellar
mass. These galaxies seem to be truly unique, as they do not follow the
characteristic kinematical and stellar population patterns of present-day
massive ellipticals, spirals or even dwarfs.Comment: 16 pages, 11 figures; Accepted for publication in MNRA
Galaxy Harassment and the Evolution of Clusters of Galaxies
Disturbed spiral galaxies with high rates of star formation pervaded clusters
of galaxies just a few billion years ago, but nearby clusters exclude spirals
in favor of ellipticals. ``Galaxy harassment" (frequent high speed galaxy
encounters) drives the morphological transformation of galaxies in clusters,
provides fuel for quasars in subluminous hosts and leaves detectable debris
arcs. Simulated images of harassed galaxies are strikingly similar to the
distorted spirals in clusters at observed by the Hubble Space
Telescope.Comment: Submitted to Nature. Latex file, 7 pages, 10 photographs in gif and
jpeg format included. 10 compressed postscript figures and text available
using anonymous ftp from ftp://ftp-hpcc.astro.washington.edu/pub/hpcc/moore/
(mget *) Also available at http://www-hpcc.astro.washington.edu/papers
The intermediate-redshift galaxy cluster CL 0048-2942. Stellar populations
We present a detailed study of the cluster CL 0048-2942, located at z~0.64,
based on a photometric and spectroscopic catalogue of 54 galaxies in a 5 x 5
square arcmin region centred in that cluster. Of these, 23 galaxies were found
to belong to the cluster. Based on this sample, the line-of-sight velocity
dispersion of the cluster is approximately 680 +- 140 km/s. We have performed
stellar population synthesis in the cluster members as well as in the field
galaxies of the sample and found that there are population gradients in the
cluster with central galaxies hosting mainly intermediate/old populations
whereas galaxies in the cluster outskirts show clearly an increase of younger
populations, meaning that star formation is predominantly taking place in the
outer regions of the cluster. In a general way, field galaxies seem to host
less evolved stellar populations than cluster members. In fact, in terms of
ages, young supergiant stars dominate the spectra of field galaxies whereas
cluster galaxies display a dominant number of old and intermediate age stars.
Following the work of other authors (e.g. Dressler et al. 1999) we have
estimated the percentage of K+A galaxies in our sample and found around 13% in
the cluster and 10% in the field. These values were estimated through means of
a new method, based on stellar population synthesis results, that takes into
account all possible absorption features in the spectrum and thus makes optimal
use of the data.Comment: Accepted by Astronomy & Astrophysics. 24 pages, 10 figures, 10 tables
(figures 3, 4, 5 and tables 1, 3, 4, 5, 6, 7, 8 will be available in
electronic format only in the A&A published version
The Fundamental Plane of Early Type Galaxies in Nearby Clusters from the WINGS Database
By exploting the data of three large surveys (WINGS, NFPS and SDSS), we
present here a comparative analysis of the Fundamental Plane (FP hereafter) of
the early-type galaxies (ETGs) belonging to 59 galaxy clusters in the redshift
range .
We show that the variances of the distributions of the FP coefficients
derived for the clusters in our sample are not consistent with the hypothesis
of universality of the FP relation. By investigating the origin of such
remarkable variances we find that, besides a couple of obvious factors, such as
the adopted fitting technique and the method used to measure the photometric
and kinematic variables, the coefficients of the FP are strongly influenced by
a number of things, mainly related to the distribution of photometric/kinematic
properties of galaxies in the particular sample under analysis. For instance,
the coefficient derived for the whole sample of ETGs, turns out to decrease
when faint galaxies are progressively removed from the sample, suggesting that
bright and faint ETGs have systematically different FPs, likely because of
different mechanisms of galaxy formation. In general, by comparing mock cluster
samples with the real one, we conclude that the observed variances of the FP
coefficients cannot be attributed just to statistical uncertainties. We
speculate that the FP is actually a bent surface, which is approximated by
different planes when different selection criteria, either chosen or induced by
observations, are acting to define galaxies samples.
We also find ...Comment: 51 pages, 18 figures, ApJ submitte
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