The Star Cluster System in the Nearby Starburst Galaxy M82

TL;DR

This study analyzes the properties, ages, and spatial distribution of over a thousand star clusters in M82, revealing recent disk-wide star formation around 500 Myr ago and identifying old globular clusters in the halo.

Contribution

First comprehensive photometric analysis of M82's star clusters across multiple bands, revealing their age distribution, spatial structure, and implications for galaxy interaction history.

Findings

Most disk clusters are 100 Myr to 1 Gyr old, peaking at 500 Myr.

Halo clusters are older than 1 Gyr, similar to Milky Way globulars.

Disk clusters follow a power-law luminosity function with index -2.04.

Abstract

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.