THE AGE, MASS, AND SIZE DISTRIBUTIONS OF STAR CLUSTERS IN M51

We present a new catalog of 3816 compact star clusters in the grand design spiral galaxy M51 based on observations taken with the Hubble Space Telescope. The age distribution of the clusters declines starting at very young ages, and can be represented by a power law, dN/dT alpha T-gamma), with gamma = -0.65 +/- 0.15. No significant changes in the shape of the age distribution at different masses is observed. The mass function of the clusters younger than T approximate to 400 Myr can also be described by a power law, dN/dM alpha M-beta, with beta approximate to -2.1 +/- 0.2. We compare these distributions with the predictions from various cluster disruption models, and find that they are consistent with models where clusters disrupt approximately independent of their initial mass, but not with models where lower mass clusters are disrupted earlier than their higher mass counterparts. We find that the half-light radii of clusters more massive than M approximate to 3 x 10(4) M-circle dot and with ages between 100 and 400 Myr are larger by a factor of approximate to 3-4 than their counterparts that are younger than 10(7) years old, suggesting that the clusters physically expand during their early life.