Cluster Galaxies Die Hard
  We investigate how the specific star formation rates of galaxies of different
masses depend on cluster-centric radius and on the central/satellite dichotomy
in both field and cluster environments. Recent data from a variety of sources,
including the cluster catalogue of von der Linden et al. are compared to the
semi-analytic models of De Lucia & Blaizot. We find that these models predict
too many passive satellite galaxies in clusters, too few passive central
galaxies with low stellar masses, and too many passive central galaxies with
high masses. We then outline a series of modifications to the model necessary
to solve these problems: a) Instead of instantaneous stripping of the external
gas reservoir after a galaxy becomes a satellite, the gas supply is assumed to
decrease at the same rate that the surrounding halo loses mass due to tidal
stripping, b) The AGN feedback efficiency is lowered to bring the fraction of
massive passive centrals in better agreement with the data. We also allow for
radio mode AGN feedback in satellite galaxies. c) We assume that satellite
galaxies residing in host haloes with masses below 10^12 M_sun do not undergo
any stripping. We highlight the fact that in low mass galaxies, the external
reservoir is composed primarily of gas that has been expelled from the galactic
disk by supernovae driven winds. This gas must remain available as a future
reservoir for star formation, even in satellite galaxies. Finally, we present a
simple recipe for the stripping of gas and dark matter in satellites that can
be used in models where subhalo evolution is not followed in detail.
