Gemini Spectroscopic Survey of Young Star Clusters in
  Merging/Interacting Galaxies. III. The Antennae
  We present optical spectroscopy of 16 star clusters in the merging galaxies
NGC 4038/39 ("The Antennae") and supplement this dataset with HST imaging. The
age and metallicity of each cluster is derived through a comparison between the
observed Balmer and metal line strengths with simple stellar population models.
We then estimate extinctions and masses using the photometry. We find that all
but three clusters have ages between ~3-200 Myr, consistent with the expected
increase in the star-formation rate due to the merger. Most of the clusters
have velocities in agreement with nearby molecular and HI gas that has been
previously shown to be rotating within the progenitor galaxies, hence
star/cluster formation is still taking place within the galactic disks.
However, three clusters have radial velocities that are inconsistent with being
part of the rotating gas disks, which is surprising given their young
(200-500Myr) ages. Interestingly, we find a stellar association with the same
colors (V-I) near one of these three clusters, suggesting that the cluster and
association were formed concurrently and have remained spatially correlated. We
find evidence for spatially distributed cluster formation throughout the
duration of the merger. The impact of various assumptions about the
star/cluster formation rate on the interpretation of the cluster age
distribution are explored, and we do not find evidence for long term "infant
mortality" as has been previously suggested. Models of galaxy mergers that
include a prescription for star formation can provide an overall good fit to
the observed cluster age distribution.
