Newly Identified Star Clusters in M33. II. Radial HST/ACS Fields

TL;DR

This study presents new photometric data for 161 star clusters in M33, including 115 newly cataloged, extending the cluster catalog depth and providing age and mass estimates based on HST observations.

Contribution

The paper provides the first comprehensive photometric analysis of a large sample of M33 clusters using HST, including 115 new clusters and detailed age and mass estimates.

Findings

115 new star clusters identified and cataloged.

Cluster ages range from 10 million to 1 billion years.

Cluster masses estimated between 5,000 and 50,000 solar masses.

Abstract

We present integrated photometry and color-magnitude diagrams for 161 star clusters in M33, of which 115 were previously uncataloged, using the Advanced Camera For Surveys Wide Field Channel onboard the Hubble Space Telescope. The integrated V-band magnitudes of these clusters range from Mv~-9 to as faint as Mv~-4, extending the depth of the existing M33 cluster catalogs by ~1 mag. Comparisons of theoretical isochrones to the color-magnitude diagrams using the Padova models yield ages for 148 of these star clusters. The ages range from Log (t)~7.0 to Log (t)~9.0. Our color-magnitude diagrams are not sensitive to clusters older than ~1 Gyr. We find that the variation of the clusters' integrated colors and absolute magnitudes with age is consistent with the predictions of simple stellar population models. These same models suggest that the masses of the clusters in our sample range from 5x10^3 to 5x10^4 *Msun.