Star clusters in the starburst galaxy M82

We present a study of star clusters in the starburst galaxy M82 using the BVI mosaic images taken with the Hubble Space Telescopeʹs Advanced Camera for Surveys. We have selected about 850 clusters with V < 23 mag based on their morphological information. The brightest cluster is as bright as V ~ 16.5 mag (MV ~ —11.2 mag) and most clusters are fainter than V = 18 mag (MV = —9.7 mag). The V-band luminosity function is represented by a power law with a slope a ~ —2.0 in the range of —9.5 < MV < —7 mag. The star clusters in M82 are mainly distributed in the galaxyʹs disk. However, about a dozen clusters are found far from the disk and are considered to belong to the halo of M82. The color-magnitude diagrams of star clusters show that most star clusters are highly reddened. We have derived the age of the star clusters using a spectral-energy-distribution fitting method with Bruzual & Charlot simple stellar population models. We discuss the age distribution as well as the photometric properties of the star clusters in regard to the formation history of the M82 cluster population.