Stellar Populations and Radial Migrations in Virgo Disk Galaxies
  We present stellar age profiles for 64 Virgo cluster disk galaxies whose
analysis poses a challenge for current galaxy formation models. Our results can
be summarized as follows: first, and contrary to observations of field
galaxies, these cluster galaxies are distributed almost equally amongst the
three main types of disk galaxy luminosity profiles (I/II/III), indicating that
the formation and/or survival of Type II breaks is suppressed within the
cluster environment. Second, we find examples of statistically-significant
inversions ("U-shapes") in the age profiles of all three disk galaxy types,
reminescent of predictions from high-resolution simulations of
classically-truncated Type II disks in the field. These features characterize
the age profiles for only about a third (<36%) of each disk galaxy type in our
sample. An even smaller fraction of cluster disks (~11% of the total sample),
exhibit age profiles which decrease outwards (i.e., negative age gradients).
Instead, flat and/or positive age gradients prevail (>50%) within our Type I,
II and III sub-samples. These observations thus suggest that while stellar
migrations and inside-out growth can play a significant role in the evolution
of all disk galaxy types, other factors contributing to the evolution of
galaxies can overwhelm the predicted signatures of these processes. We
interpret our observations through a scenario whereby Virgo cluster disk
galaxies formed initially like their bretheren in the field but which, upon
falling into the cluster, were transformed into their present state through
external processes linked to the environment. Current disk galaxy formation
models fail to reproduce these results, thus calling for adequate
hydrodynamical simulations of dense galaxy environments, for which the current
paper provides many constraints. [Abridged]
