Gas expulsion in highly substructured embedded star clusters

TL;DR

This study models the response of highly substructured embedded star clusters to gas expulsion, showing that the virial ratio of stars alone predicts cluster survival with high accuracy and suggesting gas removal isn't the primary cause of cluster dissolution.

Contribution

Introduces a simple analytical method to estimate cluster mass retention post-gas expulsion based on stellar virial ratio, accounting for complex substructure and realistic gas treatment.

Findings

Virial ratio of stars predicts mass retention within 10%.

Substructure prolongs subvirial states, aiding cluster survival.

Gas expulsion alone is unlikely to dissolve young clusters.

Abstract

We investigate the response of initially substructured, young, embedded star clusters to instantaneous gas expulsion of their natal gas. We introduce primordial substructure to the stars and the gas by simplistically modelling the star formation process so as to obtain a variety of substructure distributed within our modelled star forming regions. We show that, by measuring the virial ratio of the stars alone (disregarding the gas completely), we can estimate how much mass a star cluster will retain after gas expulsion to within 10% accuracy, no matter how complex the background structure of the gas is, and we present a simple analytical recipe describing this behaviour. We show that the evolution of the star cluster while still embedded in the natal gas, and the behavior of the gas before being expelled, are crucial processes that affect the timescale on which the cluster can evolve into a virialized spherical system. Embedded star clusters that have high levels of substructure are subvirial for longer times, enabling them to survive gas expulsion better than a virialized and spherical system. By using a more realistic treatment for the background gas than our previous studies, we find it very difficult to destroy the young clusters with instantaneous gas expulsion. We conclude that gas removal may not be the main culprit for the dissolution of young star clusters.