What determines the mass of the most massive star cluster in a galaxy: statistics, physics or disruption?

TL;DR

This paper investigates what influences the maximum mass of star clusters in galaxies, examining statistical, physical, and disruption factors, and challenges some existing disruption models by analyzing observational data and luminosity functions.

Contribution

It demonstrates that the maximum cluster mass is primarily determined by sample size and physical limits, and introduces a method to distinguish between disruption effects and mass function truncations.

Findings

M_max correlates with the number of clusters in most galaxies.

Massive clusters are more stable than predicted by mass-independent disruption models.

A physical upper limit to cluster mass exists around 10^6 solar masses in some galaxies.

Abstract

In many different galactic environments the cluster initial mass function (CIMF) is well described by a power-law with index -2. This implies a linear relation between the mass of the most massive cluster (M_max) and the number of clusters. Assuming a constant cluster formation rate and no disruption of the most massive clusters it also means that M_max increases linearly with age when determining M_max in logarithmic age bins. We observe this increase in five out of the seven galaxies in our sample, suggesting that M_max is determined by the size of the sample. It also means that massive clusters are very stable against disruption, in disagreement with the mass independent disruption (MID) model presented at this conference. For the clusters in M51 and the Antennae galaxies the size-of-sample prediction breaks down around 10^6 M_sun, suggesting that this is a physical upper limit to the masses of star clusters in these galaxies. In this method there is a degeneracy between MID and a CIMF truncation. We show how the cluster luminosity function can serve as a tool to distinguish between the two.