Galaxy evolution in the cluster Abell 85: new insights from the dwarf population

We present the first results of a new spectroscopic survey of the cluster Abell 85 targeting 1466 candidate cluster members within the central similar to 1 deg(2) of the cluster and having magnitudes m(r) < 20.5 using the VIsible MultiObject Spectrograph on the VLT and the Hydra spectrograh on WIYN. A total of 520 galaxies are confirmed as either relaxed cluster members or part of an infalling population. A significant fraction are low mass; the median stellar mass of the sample is 10(9.6)M(circle dot), and 25 per cent have stellar masses below 10(9) M-circle dot (i.e. 133 dwarf galaxies). We also identify seven active galactic nuclei (AGN), four of which reside in dwarf host galaxies. We probe the evolution of star formation rates, based on Ha emission and continuum modelling, as a function of both mass and environment. We find that more star-forming galaxies are observed at larger clustercentric distances, while infalling galaxies show evidence for recently enhanced star-forming activity. Main-sequence galaxies, defined by their continuum star formation rates, show different evolutionary behaviour based on their mass. At the low-mass end, the galaxies have had their star formation recently quenched, while more massive galaxies show no significant change. The time-scales probed here favour fast quenching mechanisms, such as ram-pressure stripping. Galaxies within the green valley, defined similarly, do not show evidence of quenching. Instead, the low-mass galaxies maintain their levels of star-forming activity, while the more massive galaxies have experienced a recent burst.