The dwarf galaxy population in Abell 2218

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 approximate to -13.2 mag, mu(0) approximate to 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 = -1.23 +/- 0.13 within the projected central core of the cluster (100 < r < 300 h(-1) kpc) to alpha = -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.