Mass-radius relation of intermediate-age disk super star clusters of M82

TL;DR

This study analyzes the structural properties and evolution of 99 intermediate-age super star clusters in M82, revealing their mass-radius relation, survival prospects, and comparison with globular clusters.

Contribution

It provides the first comprehensive structural and dynamical analysis of M82's SSCs, including their mass-radius relation and long-term survival predictions.

Findings

SSCs follow a power-law mass function with index 1.5.

Most clusters are expanding and will dissolve in ~2 Gyr.

A small group of clusters may survive for a Hubble time.

Abstract

We present a complete set of structural parameters for a sample of 99 intermediate-age Super Star Cluster (SSCs) in the disk of M82, and carry out a survival analysis using the semi-analytical cluster evolution code EMACSS. The parameters are based on the profile-fitting analysis carried out in a previous work, with the mass-related quantities derived using a mass-to-light ratio for a constant age of 100 Myr. The SSCs follow a power-law mass function with an index ${\alpha}$=1.5, and a log-normal size function with a typical half-light radius, Rh=4.3 pc, which are both comparable with the values for clusters in the Magellanic Clouds, rather than in giant spirals. The majority of the SSCs follow a power-law mass-radius relation with an index of b=0.29${\pm}$0.05. A dynamical analysis of M82 SSCs using EMACSS suggests that 23% of the clusters are tidally-limited, with the rest undergoing expansion at present. Forward evolution of these clusters suggests that the majority would dissolve in ~2 Gyr. However, a group of four massive compact clusters, and another group of five SSCs at relatively large galactocentric distances, are found to survive for a Hubble time. The model-predicted mass, Rh, ${\mu_V}$ and core radius of these surviving SSCs at 12 Gyr are comparable with the corresponding values for the sample of Galactic globular clusters.