595 research outputs found
Deep Luminosity Functions and Colour-Magnitude Relations for Cluster Galaxies at 0.2 < z < 0.6
We derive deep band luminosity functions and colour-magnitude diagrams
from HST imaging for eleven clusters observed at various stages of
merging, and a comparison sample of five more relaxed clusters at similar
redshifts. The characteristic magnitude evolves passively out to ,
while the faint end slope of the luminosity function is at all
redshifts. Cluster galaxies must have been completely assembled down to out to . We observe tight colour-magnitude relations over a
luminosity range of up to 8 magnitudes, consistent with the passive evolution
of ancient stellar populations. This is found in all clusters, irrespective of
their dynamical status (involved in a collision or not, or even within
subclusters for the same object) and suggests that environment does not have a
strong influence on galaxy properties. A red sequence luminosity function can
be followed to the limits of our photometry: we see no evidence of a weakening
of the red sequence to . The blue galaxy fraction rises with redshift,
especially at fainter absolute magnitudes. We observe bright blue galaxies in
clusters at that are not encountered locally. Surface brightness
selection effects preferentially influence the detectability of faint red
galaxies, accounting for claims of evolution at the faint end.Comment: 21 pages. A series of figures for individual clusters (the full
sample) will be made available on the MNRAS website. Accepted by MNRA
Morphological evolution in situ: Disk-dominated cluster red sequences at z ~ 1.25
We have carried out a joint photometric and structural analysis of red
sequence galaxies in four clusters at a mean redshift of z ~ 1.25 using optical
and near-IR HST imaging reaching to at least 3 magnitudes fainter than .
As expected, the photometry and overall galaxy sizes imply purely passive
evolution of stellar populations in red sequence cluster galaxies. However, the
morphologies of red sequence cluster galaxies at these redshifts show
significant differences to those of local counterparts. Apart from the most
massive galaxies, the high redshift red sequence galaxies are significantly
diskier than their low redshift analogues. These galaxies also show significant
colour gradients, again not present in their low redshift equivalents, most
straightforwardly explained by radial age gradients. A clear implication of
these findings is that red sequence cluster galaxies originally arrive on the
sequence as disk-dominated galaxies whose disks subsequently fade or evolve
secularly to end up as high S\'ersic index early-type galaxies (classical S0s
or possibly ellipticals) at lower redshift. The apparent lack of growth seen in
a comparison of high and low redshift red sequence galaxies implies that any
evolution is internal and is unlikely to involve significant mergers. While
significant star formation may have ended at high redshift, the cluster red
sequence population continues to evolve (morphologically) for several Gyrs
thereafter.Comment: Accepted by MNRA
A panchromatic survey of post-starburst mergers: searching for feedback
We consider the morphology, stellar populations, structure and AGN activity of 10 post-starburst (K+A) galaxies with Hubble Space Telescope (HST) observations, full spectral coverage in the optical, spectral energy distributions from 0.2 to 160 mu m, X-ray and radio data. Our results show that the post-starburst galaxy (PSG) phenomenon is related to mergers and interactions, and that star formation was likely triggered during close passes prior to final coalescence. We performed a detailed qualitative analysis of the observed light distribution, including low surface brightness tidal features and colour profiles, in high-resolution multiband imaging with HST. We find evidence that star formation was centrally concentrated and that quenching took place from the inside-out, consistent with the occurrence of a feedback episode. Most of our PSGs contain massive bulges and therefore should host supermassive black holes. We search for AGN activity in spectra (line ratios), optical variability, X-ray emission at 0.5-7.0 KeV and radio emission at 20 cm: all four lines of evidence show that there is no active AGN accreting at more than 0.1 per cent of the Eddington luminosity. We conclude that mergers may be a necessary, but not a sufficient condition, for AGN activity and that they are not likely to be important in our objects. If PSGs are good test cases for quenching and evolution to the red sequence, AGNs may play a smaller role than expected.</p
The K-selected Butcher-Oemler Effect
[abridged] We investigate the Butcher-Oemler effect in a sample of K-selected
galaxies in 33 clusters at 0.15 < z < 0.92. We attempt to duplicate the
original Butcher-Oemler analysis as closely as possible given the
characteristics of our data. We find that the infrared selected blue fractions
are lower than those measured in the optical and that the trend with redshift
is much weaker. Comparison with optical data in clusters in common with Butcher
& Oemler (1984) shows that infrared selection is the primary difference between
our study and optically selected samples. We suggest that the Butcher-Oemler
effect is in large part due to a population of star-forming low mass galaxies
which will evolve into dwarf galaxies. These early results point to the need
for larger and deeper infrared samples of cluster galaxies to address this
issueComment: 37 pages, 19 figures, ApJ accepted (vol 598 n1
Scaling relations of the colour-detected cluster RzCS 052 at z=1.016 and of some other high redshift clusters
We report on the discovery of the z=1.016 cluster RzCS 052 using a modified
red sequence method, followup spectroscopy and X-ray imaging. This cluster has
a velocity dispersion of 710+-150 km/s, a virial mass of 4.0e14 Msol (based on
21 spectroscopically confirmed members) and an X-ray luminosity of (0.68+-
0.47)e44 ergs/s in the [1-4] keV band. This optically selected cluster appears
to be of richness class 3 and to follow the known L_X-sigma_v relation for high
redshift X-ray selected clusters. Using these data, we find that the halo
occupation number for this cluster is only marginally consistent with what
expected assuming a self-similar evolution of cluster scaling relations,
suggesting perhaps a break of them at z~1. We also rule out a strong galaxy
merging activity between z=1 and today. Finally, we present a Bayesian approach
to measuring cluster velocity dispersions and X-ray luminosities in the
presence of a background: we critically reanalyze recent claims for X-ray
underluminous clusters using these techniques and find that the clusters can be
accommodated within the existing L_X -sigma_v relation.Comment: MNRAS, in pres
The cluster galaxy luminosity function at : a recent origin for the faint-end upturn ?
We derive deep luminosity functions (to ) for galaxies in Abell 1835
() and AC 114 () and compare these with the local
luminosity function for 69 clusters. The data show that the faint-end upturn,
the excess of galaxies above a single Schechter function at , does
not exist in the higher redshift clusters. This suggests that the faint-end
upturn galaxies have been created recently, by infall into clusters of
star-forming field populations or via tidal disruption of brighter objects.^MComment: 6 pages, MNRAS main journal, accepted for publicatio
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