Galaxy Evolution in the Environment of ABCG 209

We examine the environmental effects on the photometric properties of galaxies for the rich galaxy cluster ABCG 209 at z = 0.209. We use archive CFHT optical imaging of a 42 × 28 arcmin 2 field centred on the cluster to produce a galaxy sample complete to B = 25.0 and R = 24.5. Both the composite and red sequence galaxy luminosity functions are found to be dependent on the local galaxy surface density, their faint-end slopes becoming shallower with increasing density. We explain this as a combination of the morphology-density relation, and dwarf galaxies being cannibalised and/or disrupted by the cD galaxy and the ICM in the cluster core. The B − R colour of the red sequence itself appears 0.02 mag redder for the highest-density regions, indicative of their stellar populations being marginally (< 5%) older or (< 20%) more metal-rich. This may be due to the galaxies themselves forming earliest in the rarest overdensities marked by rich clusters, or their star-formation being suppressed earliest by the ICM.