The effect of the dynamical state of clusters on gas expulsion and infant mortality

TL;DR

This paper argues that the dynamical state of stars in a cluster prior to gas expulsion, rather than star formation efficiency, determines the cluster's survival, highlighting the importance of initial stellar velocities.

Contribution

It challenges the traditional view by emphasizing the pre-expulsion dynamical state over SFE as the key factor for cluster survivability.

Findings

Dynamical state (virial ratio) before gas expulsion is critical.

Even slightly cold initial conditions enhance cluster survival.

SFE alone is not the decisive factor for cluster longevity.

Abstract

The star formation efficiency (SFE) of a star cluster is thought to be the critical factor in determining if the cluster can survive for a significant (>50 Myr) time. There is an often quoted critical SFE of ~30 per cent for a cluster to survive gas expulsion. I reiterate that the SFE is not the critical factor, rather it is the dynamical state of the stars (as measured by their virial ratio) immediately before gas expulsion that is the critical factor. If the stars in a star cluster are born in an even slightly cold dynamical state then the survivability of a cluster can be greatly increased.