The Star Cluster Population of the Collisional Ring Galaxy NGC 922
  We present a detailed study of the star cluster population detected in the
galaxy NGC922, one of the closest collisional ring galaxies known to date,
using HST/WFPC2 UBVI photometry, population synthesis models, and N-body/SPH
simulations.We find that 69% of the clusters are younger than 7Myr, and that
most of them are located in the ring or along the bar, consistent with the
strong Halpha emission. The cluster luminosity function slope of 2.1-2.3 for
NGC922 is in agreement with those of young clusters in nearby galaxies. Models
of the cluster age distribution match the observations best when cluster
disruption is considered. We also find clusters with ages (>50Myr) and masses
(>10^5 Msun) that are excellent progenitors for faint fuzzy clusters. The
images also show a tidal plume pointing toward the companion. Its stellar age
from our analysis is consistent with pre-existing stars that were stripped off
during the passage of the companion. Finally, a comparison of the star-forming
complexes observed in NGC922 with those of a distant ring galaxy from the GOODS
field indicates very similar masses and sizes, suggesting similar origins.
