A Catalog of Bright Star Clusters in the Interacting Galaxy M51

We present a catalog of star clusters with V _F555W < 23 mag detected in the interacting spiral galaxy M51 system based on mosaic images taken with the Hubble Space Telescope Advanced Camera for Surveys by the Hubble Heritage Team. We have selected about 3600 clusters based on their morphological information through visual inspection. The final star cluster catalog includes 2224 clusters that are relatively well isolated and have a circular shape. The star clusters in M51 are mostly distributed around the spiral arms of NGC 5194. The color-magnitude diagrams show that most of the star clusters in M51 are bluer than (B _F435W - V _F555W) = 0.5 and (V _F555W - I _F814W) = 0.8. There are also some red star clusters with (B _F435W - V _F555W)>0.7, uniformly distributed over the M51 field. Some of these red clusters are suspected to be a part of the halo or old disk population based on their old ages (t >= 10⁹ yrs) and their spatial distribution. The luminosity function of the star clusters is well fitted by a single power law with α = -2.59 +/- 0.03 for the range -10.0 < M_V < -8.0 mag. We find that the size distribution of the star clusters can be fitted with three Gaussian components with peaks at effective radii of 2.27, 4.80, and 7.51 pc. Some large star clusters with red color are faint fuzzy clusters, and they are distributed not only around NGC 5195 but also around NGC 5194. These faint fuzzies are found to display an elongated spatial distribution, while the normal compact red clusters show a relatively uniform distribution around NGC 5194.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.