Caught in the act: Cluster `k+a' galaxies as a link between spirals and
  S0s
  We use integral field spectroscopy of 13 disk galaxies in the cluster AC114
at z ~ 0.31 in an attempt to disentangle the physical processes responsible for
the transformation of spiral galaxies in clusters. Our sample is selected to
display a dominant young stellar population, as indicated by strong Hdelta
absorption lines in their integrated spectra. Most of our galaxies lack the
[OII] emission line, and hence ongoing star formation. They therefore possess
`k+a' spectra, indicative of a recent truncation of star formation, possibly
preceded by a starburst. Disky `k+a' galaxies are a promising candidate for the
intermediate stage of the transformation from star-forming spiral galaxies to
passive S0s.
  Our observations allow us to study the spatial distributions and the
kinematics of the different stellar populations within the galaxies. We used
three different indicators to evaluate the presence of a young population: the
equivalent width of Hdelta, the luminosity-weighted fraction of A stars, and
the fraction of the galaxy light attributable to simple stellar populations
with ages between 0.5 and 1.5 Gyr. We find a mixture of behaviours, but are
able to show that in most of galaxies the last episode of star-formation
occured in an extended disk, similar to preceeding generations of stars, though
somewhat more centrally concentrated.
  We thus exclude nuclear starbursts and violent gravitational interactions as
causes of the star formation truncation. Gentler mechanisms, such as
ram-pressure stripping or weak galaxy-galaxy interactions, appear to be
responsible for ending star-formation in these intermediate-redshift cluster
disk galaxies.
