Compact star clusters in the m31 disk

Abstract

We have carried out a survey of compact star clusters (apparent size ≲3″) in the southwest part of the M31 galaxy, based on the high-resolution Suprime-Cam images (175 × 285), covering 15% of the deprojected galaxy disk area. The UBVRI photometry of 285 cluster candidates (V ≲ 20.5 mag) was performed using frames of the Local Group Galaxies Survey. The final sample, containing 238 high probability star cluster candidates (typical half-light radius rh 1.5 pc), was selected by specifying a lower limit of rh ≳ 015 (≳0.6 pc). We derived cluster parameters based on the photometric data and multiband images by employing simple stellar population models. The clusters have a wide range of ages from 5 Myr (young objects associated with 24 μm and/or Hα emission) to 10 Gyr (globular cluster candidates), and possess mass in a range of 3.0 ≲ log(m/m) ≲ 4.3 peaking at m 4000 m. Typical age of these intermediate-mass clusters is in the range of 30 Myr ≲ t ≲ 3 Gyr, with a prominent peak at 70 Myr. These findings suggest a rich intermediate-mass star cluster population in M31, which appears to be scarce in the Milky Way galaxy. © 2009. The American Astronomical Society. All rights reserved.