323 research outputs found
How Galaxies Disguise Their Ages
We calculate the contribution to Balmer line indices from far ultraviolet
component sources. We find that this is significant, and may lead to
identification of spurious age differences of the order of a total span of
Gyrs or size bursts observed a few Gyrs after star
formation stops. We suggest that claims for intermediate age populations in
early-type galaxies may need to be reconsidered in the light of this new
evidence.Comment: Accepted by MNRA
AGB populations in post-starburst galaxies
In a previous paper we compared the SEDs of a sample of 808 K+A galaxies from
the FUV to the MIR to the predictions of the spectrum synthesis models
explicitly using AGB components. Here we use the new AGB-light models from C.
Maraston (including less fuel for the later stages of stellar evolution and
improved calibrations) to address the discrepancies between our observations
and the AGB-heavy models used in our previous paper, which over-predict the
infrared fluxes of post-starburst galaxies by an order of magnitude. The new
models yield a much better fit to the data, especially in the near-IR, compared
to previous realizations where AGB stars caused a large excess in the H and K
bands. We { also compare the predictions of the M2013 models to those with BC03
and find that both reproduce the observations equally well. } We still find a
significant discrepancy with { both sets of models} in the Y and J bands, which
however is probably due to the spectral features of AGB stars. We also find
that { both the M2013 and the BC03 models} still over-predict the observed
fluxes in the UV bands, even invoking extinction laws that are stronger in
these bands. While there may be some simple explanations for this discrepancy,
we find that further progress requires new observations and better modelling.
Excess mid-infrared emission longward of 5m is well modelled by a
Black-Body, which may arise from dust emission from the
circumstellar envelopes of Oxygen rich M stars (expected for a metal-rich
population of AGB stars).Comment: A&A accepte
Luminosity functions of cluster galaxies: The Near-ultraviolet luminosity function at
We derive NUV luminosity functions for 6471 NUV detected galaxies in 28 clusters and consider their dependence on cluster properties. We
consider optically red and blue galaxies and explore how their NUV LFs vary in
several cluster subsamples, selected to best show the influence of environment.
Our composite LF is well fit by the Schechter form with and in good agreement with values for the Coma
centre and the Shapley supercluster, but with a steeper slope and brighter
than in Virgo. The steep slope is due to the contribution of massive
quiescent galaxies that are faint in the NUV. There are significant differences
in the NUV LFs for clusters having low and high X-ray luminosities and for
sparse and dense clusters, though none are particularly well fitted by the
Schechter form, making a physical interpretation of the parameters difficult.
When splitting clusters into two subsamples by X-ray luminosity, the ratio of
low to high NUV luminosity galaxies is higher in the high X-ray luminosity
subsample (i.e the luminosity function is steeper across the sampled luminosity
range). In subsamples split by surface density, when characterised by Schechter
functions the dense clusters have an about a magnitude fainter than that
of the sparse clusters and is steeper ( vs.
respectively). The differences in the data appear to be driven by changes in
the LF of blue (star-forming) galaxies. This appears to be related to
interactions with the cluster gas [abridged]Comment: Accepted A&
Environmental Effects on the UV Upturn in Local Clusters of Galaxies
We explore the dependence of UV upturn colours in early type cluster galaxies
on the properties of their parent clusters (such as velocity dispersion and
X-ray luminosity) and on the positions and kinematics of galaxies within them.
We use a sample of 24 nearby clusters with highly complete spectroscopy and
optical/infrared data to select a suitable sample of red sequence galaxies,
whose FUV and NUV magnitudes we measure from archival GALEX data. Our results
show that the UV upturn colour has no dependence on cluster properties and has
the same range in all clusters. There is also no dependence on the projected
position within clusters or on line-of-sight velocity. Therefore, our
conclusion is that the UV upturn phenomenon is an intrinsic feature of cluster
early type galaxies, irrespective of their cluster environment.Comment: 8 pages. Accepted for publication MNRA
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
- …