Star Clusters in Interacting Galaxies: The Case of M51

Abstract.

We present the results of an analysis of a population of stellar clusters in the interacting galaxy, M51, using HST-WFPC2 observations. The observations were made in five broad band filters; f336w (U), f439w (B), f555w (V), f675w (R), f814w (I), and transformed to the closest corresponding Cousins-Johnson filter magnitude using the equations defined by Holtzmann [5]. Only sources that were found in every filter were analysed. By comparing the spectral energy distribution (SED) of each source with those of evolutionary spectral synthesis models [4], we have derived an age, mass, and extinction for each source. The comparison was done using the 3DEF method [2], that is based on a least $\chi^2$ test. Only sources that were well-fit ( $\chi^2_\nu \le 1.0$) and resolved (fwhm $\ge 1.5$ pixels [1]) were used in this study. 533 sources pass these criteria, and will be referred to as clusters for the remainder of the paper. With this sample we are able to study the cluster formation history, the cluster initial mass function (cIMF), and search for evidence of cluster disruption.