Star Cluster Candidates in M81

TL;DR

This paper catalogs various extended objects near M81 using HST ACS imaging, identifying numerous globular clusters, HII regions, background galaxies, and unclassified objects, with some color analysis to infer their nature.

Contribution

It provides the first extensive catalog of extended objects around M81, including new globular cluster candidates and their color properties, enhancing understanding of M81's environment.

Findings

Identified 233 globular cluster candidates.

Found 92 HII regions, OB associations, or open clusters.

Cataloged 489 background galaxies.

Abstract

We present a catalog of extended objects in the vicinity of M81 based a set of 24 Hubble Space Telescope Advanced Camera for Surveys (ACS) Wide Field Camera (WFC) F814W (I-band) images. We have found 233 good globular cluster candidates; 92 candidate HII regions, OB associations, or diffuse open clusters; 489 probable background galaxies; and 1719 unclassified objects. We have color data from ground-based g- and r-band MMT Megacam images for 79 galaxies, 125 globular cluster candidates, 7 HII regions, and 184 unclassified objects. The color-color diagram of globular cluster candidates shows that most fall into the range 0.25 < g-r < 1.25 and 0.5 < r-I < 1.25, similar to the color range of Milky Way globular clusters. Unclassified objects are often blue, suggesting that many of them are likely to be HII regions and open clusters, although a few galaxies and globular clusters may be among them.