Star-forming galaxies in low-redshift clusters: Effects of environment
  on the concentration of star formation
  We attempt to determine the dominant processes acting on star-forming disk
galaxies as a result of the cluster environment by studying the normalised
rates and radial distributions of star formation in galaxies within
low-redshift clusters. We develop indicators of different processes based on
the radial concentrations of R-band and H alpha light within each of the
galaxies studied. The tests are applied to galaxies in each of 3 environments -
cluster, supercluster (outside the cluster virial radius) and field. We develop
new diagnostic diagrams combining star-formation rate and spatial distribution
information to differentiate between stripping of outer disk gas, general gas
depletion, nuclear starbursts and galaxy-wide enhancement of star formation.
Hubble type classifications of cluster galaxies are found to correlate only
weakly with their concentration indices, whereas this correlation is strong for
non-cluster populations of disk galaxies. We identify a population of
early-type disk galaxies in the cluster population with both enhanced and
centrally-concentrated star formation compared to their field counterparts. The
enhanced cluster galaxies frequently show evidence of disturbance. A small but
non-negligible population of cluster galaxies with truncation of star formation
in their outer disks is also found.
