DAWN. I. Simulating the formation and early evolution of stellar clusters with Phantom N-Body

TL;DR

This paper introduces a new simulation framework combining stellar dynamics and hydrodynamics to study early star cluster formation, enabling large statistical samples and revealing the significant impact of massive stars on cluster evolution.

Contribution

The paper presents a novel simulation framework integrating regularisation, star formation, and gas removal in Phantom N-Body, allowing efficient, large-scale studies of early stellar cluster dynamics.

Findings

Massive stars influence star formation and cluster dynamics.

Simulation methods significantly speed up calculations.

Cluster evolution shows stochastic behavior influenced by massive stars.

Abstract

Context. Simulating stellar dynamics in a molecular cloud environment is numerically challenging due to the strong coupling between young stars and their surrounding gas, and the large range of length and time scales. Aims. This paper is the first of a suite aimed at investigating the complex early stellar dynamics in star-forming regions. We present a new simulation framework which is the key to generating a larger set of simulations, enabling statistical analysis. Methods. Methods originating from the stellar dynamics community, including regularisation and slowdown methods (SDAR), have been added to the hydrodynamical code Phantom to produce simulations of embedded cluster early dynamics. This is completed by a novel prescription of star formation to initialise stars with a low numerical cost, but in a way that is consistent with the gas distribution. Finally, a prescription for H ii region expansion has been added to model the gas removal. Results. We have run testcase simulations following the dynamical evolution of stellar clusters from the cloud collapse to a few Myr. Our new numerical methods fulfil their function by speeding up the calculation. The N-body dynamics with our novel implementation never appear as a bottleneck. Our first simulations show that massive stars largely impact the star formation process and shape the dynamics of the resulting cluster. Depending on the position of these massive stars and the strength of their feedback, they can prematurely dismantle part of the cloud or trigger a second event of cloud collapse, preferentially forming low-mass stars. This stochastic behaviour confirms the need for statistical studies. Conclusions. Our new Phantom N-Body framework enables efficient simulation of the formation and evolution of star clusters. It enables the statistical analysis needed to build models of the dynamical evolution of embedded star clusters.