The puzzle of the cluster-forming core mass-radius relation and why it matters

TL;DR

This paper investigates how the mass-radius relation of cluster-forming cores influences cluster infant weight-loss and disruption, highlighting the importance of core density profiles and external tidal fields in cluster evolution.

Contribution

It introduces a model linking core mass-radius relations to cluster disruption outcomes, emphasizing the impact of core density profiles and external tidal influences.

Findings

Constant surface density cores favor high-mass cluster removal.

Constant radius cores lead to low-mass cluster removal.

Mass-independent infant weight-loss occurs with constant volume density cores.

Abstract

We highlight how the mass-radius relation of cluster-forming cores combined with an external tidal field can influence infant weight-loss and disruption likelihood of clusters after gas expulsion. Specifically, we study how the relation between the bound fraction of stars staying in clusters at the end of violent relaxation and the cluster-forming core mass is affected by the slope and normalization of the core mass-radius relation. Assuming mass-independent star formation efficiency and gas-expulsion time-scale $\tau_{GExp}/\tau_{cross}$ and a given external tidal field, it is found that constant surface density cores and constant radius cores have the potential to lead to the preferential removal of high- and low-mass clusters, respectively. In contrast, constant volume density cores result in mass-independent cluster infant weight-loss, as suggested by observations. Our modelling includes predictions about the evolution of high-mass cluster-forming cores, a regime not yet covered by the observations. An overview of various issues directly affected by the nature of the core mass-radius relation is presented (e.g. cluster mass function, galaxy star formation histories, globular cluster self-enrichment). Finally, we emphasize that observational mass-radius data-sets of dense gas regions must be handled with caution as they may be the imprint of the molecular tracer used to map them, rather than reflecting cluster formation conditions. [Abridged]