A Catalog of Bright Star Clusters in the Interacting Galaxy M51

TL;DR

This paper catalogs about 2,200 star clusters in M51 using HST images, analyzing their distribution, colors, sizes, and luminosity function to understand their properties and origins.

Contribution

It provides a detailed catalog and analysis of star clusters in M51, including their distribution, sizes, colors, and luminosity function, highlighting the presence of faint fuzzy clusters.

Findings

Most clusters are bluer than (B-V)=0.5, indicating young ages.

Luminosity function follows a power law with index -2.59.

Faint fuzzy clusters are elongated and distributed around NGC 5195 and NGC 5194.

Abstract

We present a catalog of star clusters with V_{F555W}<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 (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 >= 10^9 yrs) and their spatial distribution. The luminosity function of the star clusters is fit well by a single power law with \alpha = -2.59 \pm 0.03 for the range -10.0 <M_V < -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.