A comprehensive set of simulations studying the influence of gas expulsion on star cluster evolution

TL;DR

This study uses extensive N-body simulations to analyze how residual-gas expulsion affects star cluster survival and properties, revealing critical dependencies on gas removal timescales, efficiency, and external tidal influences.

Contribution

It provides a comprehensive grid of simulation data predicting star cluster evolution under various gas expulsion scenarios, with publicly available results for broader use.

Findings

Cluster sizes and bound mass are heavily affected by gas expulsion details.

Clusters can survive with low star formation efficiency if gas removal is slow and tidal effects are weak.

Most clusters are destroyed or lose many stars during gas expulsion, with surviving clusters expanding significantly.

Abstract

We have carried out a large set of N-body simulations studying the effect of residual-gas expulsion on the survival rate and final properties of star clusters. We have varied the star formation efficiency, gas expulsion timescale and strength of the external tidal field, obtaining a three-dimensional grid of models which can be used to predict the evolution of individual star clusters or whole star cluster systems by interpolating between our runs. The complete data of these simulations is made available on the Internet. Our simulations show that cluster sizes, bound mass fraction and velocity profile are strongly influenced by the details of the gas expulsion. Although star clusters can survive star formation efficiencies as low as 10% if the tidal field is weak and the gas is removed only slowly, our simulations indicate that most star clusters are destroyed or suffer dramatic loss of stars during the gas removal phase. Surviving clusters have typically expanded by a factor 3 or 4 due to gas removal, implying that star clusters formed more concentrated than as we see them today. Maximum expansion factors seen in our runs are around 10. If gas is removed on timescales smaller than the initial crossing time, star clusters acquire strongly radially anisotropic velocity dispersions outside their half-mass radii. Observed velocity profiles of star clusters can therefore be used as a constraint on the physics of cluster formation.