COMPACT STAR CLUSTERS IN THE M31 DISK

We have carried out a survey of compact star clusters (apparent size less than or similar to 3 '') in the southwest part of the M31 galaxy, based on the high-resolution Suprime-Cam images (17.'5 x 28.'5), covering similar to 15% of the deprojected galaxy disk area. The UBVRI photometry of 285 cluster candidates (V less than or similar to 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 r(h) similar to 1.5 pc), was selected by specifying a lower limit of r(h) greater than or similar to 0.'' 15 (greater than or similar to 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 similar to 5 Myr (young objects associated with 24 mu m and/or H alpha emission) to similar to 10 Gyr (globular cluster candidates), and possess mass in a range of 3.0 less than or similar to log(m/m(circle dot)) less than or similar to 4.3 peaking at m similar to 4000 m(circle dot). Typical age of these intermediate-mass clusters is in the range of 30 Myr less than or similar to t less than or similar to 3 Gyr, with a prominent peak at similar to 70 Myr. These findings suggest a rich intermediate-mass star cluster population in M31, which appears to be scarce in the Milky Way galaxy.