The Star Cluster System in the Nearby Starburst Galaxy M82
  We present a photometric study of star clusters in the nearby starburst
galaxy M82 based on the UBVI, YJ and H band Hubble Space Telescope images. We
find 1105 star clusters with V<23 mag. 1070 of them are located in the disk
region, while 35 star clusters are in the halo region. The star clusters in the
disk are composed of a dominant blue population with a color peak at (B-V)0 ~
0.45, and a weaker red population. The luminosity function of the disk clusters
shows a power-law distribution with a power law index alpha=-2.04+-0.03, and
the scale height of their distribution is h_z=9".64+-0".40 (164 +- 7 pc),
similar to that of the stellar thin disk of M82. We have derived the ages of
~630 star clusters using the spectral energy distribution fit method by
comparing UBVI(YJ)H band photometric data with the simple stellar population
models. The age distribution of the disk clusters shows that the most dominant
cluster population has ages ranging from 100 Myr to 1 Gyr, with a peak at about
500 Myr. This suggests that M82 has undergone a disk-wide star formation about
500 Myr ago, probably through the interaction with M81. The brightest star
clusters in the nuclear region are much brighter than those in other regions,
indicating that more massive star clusters are formed in the denser
environments. On the other hand, the colors of the halo clusters are similar to
those of globular clusters in the Milky Way Galaxy, and their ages are
estimated to be older than 1 Gyr. These are probably genuine old globular
clusters in M82.
