The dwarf galaxy population in Abell 2218

Abstract

We present results from a deep photometric study of the rich galaxy cluster Abell 2218 (z = 0.18) based on archival Hubble Space Telescope WFPC2 F606W images. These have been used to derive the luminosity function to extremely faint limits (M F606W -13.2 mag, μ 0 24.7 mag arcsec -2 ) over a wide field of view (1.3 h -2 Mpc 2 ). We find the faint-end slope of the luminosity function to vary with environment within the cluster, going from a = -1.23 ± 0.13 within the projected central core of the cluster (100 < r < 300 h -1 kpc) to a = -1.49 ± 0.06 outside this radius (300 < r < 750 h -1 kpc). We infer that the core is 'dwarf depleted', and further quantify this by studying the ratio of 'dwarf' to 'giant' galaxies and its dependency as a function of clustercentric radius and local galaxy density. We find that this ratio varies strongly with both quantities, and that the dwarf galaxy population in A2218 has a more extended distribution than the giant galaxy population.