Dwarf Galaxies in Clusters as Probes of Galaxy Formation and Dark Matter
  We present the results of a Hubble Space Telescope (HST) ACS and WFPC2 study
of dwarf galaxies in the nearby Perseus Cluster, down to M_V = -12, spanning
the core and outer regions of this cluster. We examine how properties such as
the colour magnitude relation, structure and morphology are affected by
environment for the lowest mass galaxies. The low masses of dwarf galaxies
allow us to determine their environmentally driven based galaxy evolution, the
effects of which are harder to examine in massive galaxies. The structures of
our dwarfs in both the core and outer regions of the cluster are quantified
using the concentration, asymmetry and clumpiness (CAS) parameters. We find
that, on average, dwarfs in the outer regions of Perseus are more disturbed
than those in the cluster core, with higher asymmetries and clumpier light
distributions. We measure the (V-I)_0 colours of the dEs, and find that dwarfs
in both the inner and outer regions of the cluster lie on the same colour
magnitude relation. Based on these results, we infer that the disturbed dwarfs
in the cluster outskirts are likely "transition dwarfs", with their colours
transforming before their structures. Finally, we infer from the smoothness of
the cluster core population that dwarfs in the inner regions of the cluster
must be highly dark matter dominated to prevent their disruption by the cluster
potential. We derive a new method to determine the minimum mass the dwarfs must
have to prevent this disruption without the need for resolved spectroscopy, and
determine their mass-to-light ratios. At their orbit pericentre, dwarfs in the
core of Perseus require mass-to-light ratios between 1 and 120 to prevent their
disruption, comparable to those found for the Local Group dSphs.
