552 research outputs found
Do cluster properties affect the quenching rate?
The quenching rate is known to depend on galaxy stellar mass and environment,
however, possible dependences on the hosting halo properties, such as mass,
richness, and dynamical status, are still debated. The determination of these
dependences is hampered by systematics, induced by noisy estimates of cluster
mass or by the lack of control on galaxy stellar mass, which may mask existing
trends or introduce fake trends. We studied a sample of local clusters (20 with
0.0214), selected independent of the galaxy
properties under study, having homogeneous optical photometry and X-ray
estimated properties. Using those top quality measurements of cluster mass,
hence of cluster scale, richness, iron abundance, and cooling time/presence of
a cool-core, we study the simultaneous dependence of quenching on these cluster
properties on galaxy stellar mass M and normalised cluster-centric distance
r/r200. We found that the quenching rate can be completely described by two
variables only, galaxy stellar mass and normalised cluster-centric distance,
and is independent of halo properties (mass, richness, iron abundance, presence
of a cool-core, and central cooling time). These halo properties change, in
most cases, by less than 3% the probability that a galaxy is quenched, once the
mass-size (M200-r200) scaling relation is accounted for through cluster-centric
distance normalisation.Comment: 12 pages, accepted for publication in A&
Star formation and environment in clusters up to z~2.2
The dependence of galaxy star formation activity on environment - especially
in clusters - at high redshift is still poorly understood, as illustrated by
the still limited number of z>1.4 clusters on the one hand, and by the still
debated star formation-density relation at high redshift on the other hand. The
zphot~2.2 JKCS041 cluster allows to probe such environmental dependence of star
formation activity at an unprecedented combination of redshifts and
environments. Its study permits to enlarge the knowledge of high redshift
clusters and to put strong leverage on observational constraints for galaxy
evolution models. We analyze deep u\astg'r'i'z'JHKs images from the
CFHTLS/WIRDS surveys, which cover JKCS041 cluster field. We first estimate
photometric redshifts based on multi-wavelength photometry. We then lead a
careful analysis to test the presence of a Butcher-Oemler effect. We work on
galaxies within 2\timesr200 and with masses >1.34\times10^11 Msun, and use two
comparison clusters at z=0 and z=1 of similar mass. We estimate the radial
profiles of the fraction of blue galaxies, taking into account the star aging
with decreasing redshift. After confirming the high redshift nature of JKCS041,
we find no evidence for a Butcher-Oemler effect between z~2.2 and z~0 for
galaxies more massive than 1.34\times10^11 Msun. In the cluster center, a
change greater than \Deltafblue/\Deltaz=0.16 between z~0 and z~2.2 would be
easily detected. We also find that JKCS041 shows a consistent and systematic
increase of the fraction of star-forming galaxies with cluster-centric
distance, hence with decreasing density, for both a M>1.34\times10^11 Msun
selected sample and a lower mass sample. In particular, very few (less than
15%) star-forming galaxies are found within r200/2 among high mass
(M>1.34\times10^11 Msun) galaxies. Our results show that the present-day star
formation-density relation is already in place at z~2.2.Comment: 10 pages, accepted for publication in Astronomy and Astrophysic
Deep near-infrared luminosity function of a cluster of galaxies at z=0.3
The deep near-infrared luminosity function of AC118, a cluster of galaxies at
z=0.3, is presented. AC118 is a bimodal cluster, as evidenced both by our
near-infrared images of lensed galaxies, by public X-ray Rosat images and by
the spatial distribution of bright galaxies. Taking advantage of the extension
and depth of our data, which sample an almost unexplored region in the depth
vs. observed area diagram, we derive the luminosity function (LF), down to the
dwarf regime (M*+5), computed in several cluster portions. The overall LF,
computed on a 2.66 Mpc2 areas (H_0=50 km/s/Mpc), has an intermediate slope
(alpha=-1.2). However, the LF parameters depend on the surveyed cluster region:
the central concentration has 2.6^{+5.1}_{-1.7} times more bright galaxies and
5.3^{+7.2}_{-2.3} times less dwarfs per typical galaxy than the outer region,
which includes galaxies at an average projected distance of ~580 kpc (errors
are quoted at the 99.9 % confidence level). The LF in the secondary AC118 clump
is intermediate between the central and outer one. In other words, the
near-infrared AC118 LF steepens going from high to low density regions. At an
average clustercentric distance of ~580 kpc, the AC118 LF is statistically
indistinguishable from the LF of field galaxies at similar redshift, thus
suggesting that the hostile cluster environment plays a minor role in shaping
the LF at large clustercentric distances, while it strongly affects the LF at
higher galaxy density.Comment: ApJ, in press. The whole paper with all high resolution images is
available at http://www.na.astro.it/~andreon/listapub.htm
Size growth of red-sequence early-type galaxies in clusters in the last 10 Gyr
We carried out a photometric and structural analysis in the rest-frame
band of a mass-selected () sample of red-sequence
galaxies in 14 galaxy clusters, 6 of which are at . To this end, we
reduced/analyzed about 300 orbits of multicolor images taken with the Advanced
Camera for Survey and the Wide Field Camera 3 on the Hubble Space Telescope. We
uniformly morphologically classified galaxies from to , and
we homogeneously derived sizes (effective radii) for the entire sample.
Furthermore, our size derivation allows, and therefore is not biased by, the
presence of the usual variety of morphological structures seen in early-type
galaxies, such as bulges, bars, disks, isophote twists, and ellipiticy
gradients. By using such a mass-selected sample, composed of 244 red-sequence
early-type galaxies, we find that the of the galaxy size at a fixed
stellar mass, has increased with time at a rate of
dex per Gyr over the last 10 Gyr, in marked contrast with the
threefold increase found in the literature for galaxies in the general field
over the same period. This suggests, at face value, that secular processes
should be excluded as the primary drivers of size evolution because we observed
an environmental environmental dependent size growth. Using spectroscopic ages
of Coma early-type galaxies we also find that recently quenched early-type
galaxies are a numerically minor population not different enough in size to
alter the mean size at a given mass, which implies that the progenitor bias is
minor, i.e., that the size evolution measured by selecting galaxies at the
redshift of observation is indistinguishable from the one that compares
ancestors and descendents.Comment: A&A 593, A2 (2016) after revision of the z=1.63 cluster name,
mis-typed in previous version. No result of our paper is affected by having
mis-typed the cluster nam
Is the Butcher-Oemler effect a function of the cluster redshift ?
Using PSPC {\it Rosat} data, we measure x-ray surface brightness profiles,
size and luminosity of the Butcher-Oemler (BO) sample of clusters of galaxies.
The cluster x-ray size, as measured by the Petrosian r_{\eta=2} radius, does
not change with redshift and is independent from x-ray luminosity. On the other
hand, the x-ray luminosity increases with redshift. Considering that fair
samples show no-evolution, or negative luminosity evolution, we conclude that
the BO sample is not formed from the same class of objects observed at
different look-back times. This is in conflict with the usual interpretation of
the Butcher-Oemler as an evolutionary (or redshift-dependent) effect, based on
the assumption that we are comparing the same class of objects at different
redshifts. Other trends present in the BO sample reflect selection criteria
rather than differences in look-back time, as independently confirmed by the
fact that trends loose strength when we enlarge the sample with x-ray selected
sample of clusters. The variety of optical sizes and shapes of the clusters in
the Butcher-Oemler sample, and the Malmquist-like bias, are the reasons for
these selection effects that mimic the trends usually interpreted as changes
due to evolution.Comment: ApJ, in press, scheduled on May, 10 issue. 17 pages & 11 figure
Intrinsic scatter of caustic masses and hydrostatic bias: An observational study
All estimates of cluster mass have some intrinsic scatter and perhaps some
bias with true mass even in the absence of measurement errors for example
caused by cluster triaxiality and large scale structure. Knowledge of the bias
and scatter values is fundamental for both cluster cosmology and astrophysics.
In this paper we show that the intrinsic scatter of a mass proxy can be
constrained by measurements of the gas fraction because masses with higher
values of intrinsic scatter with true mass produce more scattered gas
fractions. Moreover, the relative bias of two mass estimates can be constrained
by comparing the mean gas fraction at the same (nominal) cluster mass. Our
observational study addresses the scatter between caustic (i.e., dynamically
estimated) and true masses, and the relative bias of caustic and hydrostatic
masses. For these purposes, we used the X-ray Unbiased Cluster Sample, a
cluster sample selected independently from the intracluster medium content with
reliable masses: 34 galaxy clusters in the nearby () Universe,
mostly with , and with caustic masses.
We found a 35\% scatter between caustic and true masses. Furthermore, we found
that the relative bias between caustic and hydrostatic masses is small,
dex, improving upon past measurements. The small scatter found
confirms our previous measurements of a highly variable amount of feedback from
cluster to cluster, which is the cause of the observed large variety of
core-excised X-ray luminosities and gas masses.Comment: A&A, in press, minor language changes from previous versio
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