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

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 (SFE), gas expulsion time‐scale 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 are 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 SFEs as low as 10 per cent 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 of 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 time‐scales 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.

Dynamical constraints on the origin of multiple stellar populations in globular clusters

“…In addition, there should be a region in the parameter space in which all clusters will be totally disrupted. The outcome of our N -body simulations are consistent with Decressin et al (2010) who analysed the N -body models of Baumgardt & Kroupa (2007). As it is inferred from Fig.…”

“…The analysis of Decressin et al (2010) on the Baumgardt & Kroupa (2007) models show a similar relation between the fraction of SG stars and the number of bound stars. Since the number of bound stars is proportional to the total mass of the cluster, the result of their work matches the anti-correlation that we see in Fig.…”

“…Our simulations can be thought of as a generalized version of the Baumgardt & Kroupa (2007) models who considered the effect of gas expulsion on a single stellar population.…”

“…Any gas loss in GCs will be accompanied by loss of stars, especially when the gas loss is impulsive (Baumgardt & Kroupa 2007). There are a number of different sources which can inject enough energy into the intra-cluster medium to entirely unbind the primordial gas.…”

The Age, Mass, and Size Distributions of Star Clusters in M51

“…The amount of expansion depends on details of the gas expulsion (e.g., timescale, speed and fraction of gas that is lost, etc. ), but N-body simulations suggest that surviving clusters typically expand by a factor of 3-4 over time (Baumgardt & Kroupa 2007). This typical expansion is consistent with the evolution of sizes that we measure for clusters in M51.…”