The mmax-Mecl relation in the LEGUS clusters

TL;DR

This study models young star clusters to test the mmax-Mecl relation, finding that optimal sampling aligns with observations and supports a self-regulated cluster formation process.

Contribution

It demonstrates that the mmax-Mecl relation is consistent with optimal sampling models, challenging purely random sampling assumptions in cluster formation.

Findings

Optimal sampling matches observed cluster data.

Purely random sampling does not agree with observations.

Supports self-regulated star formation models.

Abstract

The relation between the maximum stellar mass in a very young cluster (mmax) and the total stellar mass of the cluster (Mecl), known as the mmax-Mecl relation, remains debated in the literature. To test the validity of this relation, we modelled young star clusters with masses between 102.5 and 105.0 M_sun and ages of 1-4 Myr using the galIMF code, in which stellar masses are optimally sampled from a varying initial stellar mass function. We compared the results with literature observations of extragalactic young star clusters. We incorporated stellar evolution via PARSEC and COLIBRI tracks and computed Halpha luminosities using the Pegase code. To account for dynamical ejections, we stochastically removed stars based on their spectral type, following previous N-body simulations. Additional sources of scatter, including uncertainties in age determination and contamination by field stars, were considered. Our results indicate that, under the assumptions explored here, optimal sampling is consistent with the extragalactic star cluster observations considered, whereas purely random sampling produces distributions that are not in agreement. These findings support a highly self-regulated interpretation of cluster formation in which stellar masses align optimally with the initial mass function rather than being drawn independently at random.