The difficult early stages of embedded star clusters and the importance of the pre-gas expulsion virial ratio

TL;DR

This study investigates how the initial dynamical state and gas expulsion influence the early survival of embedded star clusters through N-body simulations, highlighting the complexity of predicting cluster outcomes.

Contribution

It demonstrates the critical role of the pre-gas expulsion virial ratio and initial substructure in determining cluster survival, using detailed dynamical modeling.

Findings

Cluster survival strongly depends on initial dynamical state.

Knowledge of star-gas distribution helps estimate post-expulsion state.

Predicting cluster survival remains uncertain despite detailed information.

Abstract

We examine the effects of gas-expulsion on initially substructured distributions of stars. We perform N-body simulations of the evolution of these distributions in a static background potential to mimic the gas. We remove the static potential instantaneously to model gas-expulsion. We find that the exact dynamical state of the cluster plays a very strong role in affecting a cluster's survival, especially at early times: they may be entirely destroyed or only weakly affected. We show that knowing both detailed dynamics and relative star-gas distributions can provide a good estimate of the post-gas expulsion state of the cluster, but even knowing these is not an absolute way of determining the survival or otherwise of the cluster.