The Evolution of Substructure during Star Cluster Assembly

Abstract: Star cluster formation and assembly occurs inside filamentary and turbulent molecular clouds, which imprints both spatial and kinematic substructure on the young cluster. In this paper, we quantify the amount and evolution of this substructure in simulations of star cluster formation that include radiation magnetohydrodynamical evolution of the gas, coupled with detailed stellar dynamics, binary formation and evolution, and stellar feedback. We find that both spatial and kinematic substructure are present at early times. Both are erased as the cluster assembles through the formation of new stars as well as the merger of sub-clusters. Spatial substructure is erased over a timescale of approximately 2.5 times the initial free-fall time of the cloud. Kinematic substructure persists for longer, and is still present to the end of our simulations. We also explored our simulations for evidence of early dynamical mass segregation, and conclude that the presence of a population of binary stars can accelerate and enhance the mass segregation process.