Imprints of feedback in young gasless clusters?

TL;DR

This study uses N-body simulations to compare the long-term dynamical evolution of young star clusters formed with and without feedback, finding that initial density and virial state influence the retention of substructure.

Contribution

It provides the first detailed comparison of cluster evolution with and without feedback effects based on initial conditions from hydrodynamical simulations.

Findings

Clusters formed without feedback lose substructure over 10 Myr.

Clusters formed with feedback often retain initial substructure.

Initial density and virial state influence substructure retention.

Abstract

We present the results of N-body simulations in which we take the masses, positions and velocities of sink particles from five pairs of hydrodynamical simulations of star formation by Dale et al. (2012, 2013) and evolve them for a further 10Myr. We compare the dynamical evolution of star clusters that formed under the influence of mass-loss driven by photoionization feedback, to the evolution of clusters that formed without feedback. We remove any remaining gas and follow the evolution of structure in the clusters (measured by the Q-parameter), half-mass radius, central density, surface density and the fraction of bound stars. There is little discernible difference in the evolution of clusters that formed with feedback compared to those that formed without. The only clear trend is that all clusters which form without feedback in the hydrodynamical simulations lose any initial structure over 10Myr, whereas some of the clusters which form with feedback retain structure for the duration of the subsequent N-body simulation. This is due to lower initial densities (and hence longer relaxation times) in the clusters from Dale et al. (2012, 2013) which formed with feedback, which prevents dynamical mixing from erasing substructure. However, several other conditions (such as supervirial initial velocities) also preserve substructure, so at a given epoch one would require knowledge of the initial density and virial state of the cluster in order to determine whether star formation in a cluster has been strongly influenced by feedback.