From hydrodynamics to N-body simulations of star clusters: mergers and rotation

TL;DR

This paper introduces a new method to generate realistic initial conditions for N-body simulations of young star clusters by transforming hydrodynamical simulation outputs, enabling better study of their early evolution, mergers, and rotation.

Contribution

The paper presents a novel approach to create initial conditions for star cluster simulations from hydrodynamical data, incorporating realistic mass functions and spatial distributions.

Findings

Gas removal influences early cluster evolution.

Dry merging of sub-structures affects rotation.

Initial conditions impact dynamical evolution.

Abstract

We present a new method to obtain more realistic initial conditions for N-body simulations of young star clusters. We start from the outputs of hydrodynamical simulations of molecular cloud collapse, in which star formation is modelled with sink particles. In our approach, we instantaneously remove gas from these hydrodynamical simulation outputs to mock the end of the gas-embedded phase, induced by stellar feedback. We then enforce a realistic initial mass function by splitting or joining the sink particles based on their mass and position. Such initial conditions contain more consistent information on the spatial distribution and the kinematical and dynamical states of young star clusters, which are fundamental to properly study these systems. For example, by applying our method to a set of previously run hydrodynamical simulations, we found that the early evolution of young star clusters is affected by gas removal and by the early dry merging of sub-structures. This early evolution can either quickly erase the rotation acquired by our (sub-)clusters in their embedded phase or "fuel" it by feeding of angular momentum by sub-structure mergers, before two-body relaxation acts on longer timescales.