Young globular clusters in interacting galaxies

We have obtained deep HST images of NGC 1275 and NGC 3597 in the F450W and F702W filters. We have detected 1200 young star clusters in NGC 1275 and 700 young star clusters in NGC 3597; we propose that they are younger versions of Galactic globular clusters. In each case we detect a small spread in colors due mostly to photometric errors. We find that the small spread in colors indicates a small spread in ages for the clusters, which suggests a brief formation period due to a single catastrophic event, such as a recent merger. The luminosity function in each case shows increasing numbers of young clusters to the limits of our photometry, which extends several magnitudes past the predicted turnover in the luminosity function if these clusters are identical to Galactic globulars seen at a younger age. We theorize that this luminosity function evolves over timescales of 10 Gyr to resemble the Galactic globular cluster luminosity function through the preferential destruction of fainter, lower mass clusters. We measure the specific frequency of young globular clusters in both galaxies and find that at least in NGC 1275, the specific frequency of the merger related population is large, a requirement if this quantity can increase in a merger. We have created software to measure the structural properties of young clusters, and we find that the typical half-light radii of the young clusters in our sample are similar to the half-light radii of Galactic globulars. We find tentative evidence that the young clusters may have larger concentrations than Galactic globulars.