A Catalog of Bright Star Clusters in the Interacting Galaxy M 51 ∗

We present a catalog of star clusters with VF555W < 23 mag detected in the interacting spiral galaxy M51 system based on the mosaic images taken with HST ACS by the Hubble Heritage Team. We have selected about 3,600 clusters based on their morphological information through the visual inspection. The final star cluster catalog includes 2,224 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 (BF435W − VF555W ) = 0.5 and (VF555W − IF814W ) = 0.8. There are also some red star clusters with (BF435W − VF555W ) > 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 ≥ 10 yrs) and their spatial distribution. The luminosity function of the star clusters is fit well by a single power law with α = −2.59 ± 0.03 for the range −10.0 < MV < −8.0 mag. We find that the size distribution of the star clusters can be fit 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. Subject headings: galaxies: individual (M51; NGC5194; NGC 5195) — galaxies: spiral — galaxies: interaction — galaxies: evolution — galaxies: star clusters 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.