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 $\sim 6$ Gyrs or $\sim 15$ 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 5$\mu$m is well modelled by a $T_{dust}=300^oK$ 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

A composite K-band Luminosity Function for Cluster Galaxies

We present a composite K-band luminosity function for 10 clusters at low redshift, where member galaxies are identified from an existing spectroscopic survey (the 2dF galaxy redshift survey). Our kinematically selected K-band luminosity function is well fitted by a Schechter function with $M^*_K=-24.50 + 5\log h$ and $\alpha=-0.98$ over $-27 < <M_K -5\log h < -22$. This is very similar to the 2dF field value and suggests that the integrated mass accretion history of galaxies does not vary strongly with environmentComment: 3 pages, 1 figure, Astronomische Nachrichten (JENAM 2008 Symposium 6

Luminosity functions of cluster galaxies: The Near-ultraviolet luminosity function at <z>∼0.05<z> \sim 0.05

We derive NUV luminosity functions for 6471 NUV detected galaxies in 28 $0.02 < z < 0.08$ 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 $M^*_{NUV}=-18.98 \pm 0.07$ and $\alpha=-1.87 \pm 0.03$ in good agreement with values for the Coma centre and the Shapley supercluster, but with a steeper slope and brighter $L^*$ 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 $M^*$ about a magnitude fainter than that of the sparse clusters and $\alpha$ is steeper ($-1.9$ vs. $-1.6$ 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&

Deep Luminosity Functions and Colour-Magnitude Relations for Cluster Galaxies at 0.2 < z < 0.6

We derive deep $I$ band luminosity functions and colour-magnitude diagrams from HST imaging for eleven $0.2<z<0.6$ clusters observed at various stages of merging, and a comparison sample of five more relaxed clusters at similar redshifts. The characteristic magnitude $M^*$ evolves passively out to $z=0.6$, while the faint end slope of the luminosity function is $\alpha \sim -1$ at all redshifts. Cluster galaxies must have been completely assembled down to $M_I \sim -18$ out to $z=0.6$. 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 $z=0.6$. The blue galaxy fraction rises with redshift, especially at fainter absolute magnitudes. We observe bright blue galaxies in clusters at $z > 0.4$ 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