The long-term effects of gas removal from hydrodynamic simulations of star formation

TL;DR

This study investigates the long-term dynamical effects of gas removal in star-forming regions by combining hydrodynamic and N-body simulations, challenging previous assumptions about rapid expansion caused by feedback-driven gas expulsion.

Contribution

It introduces a novel approach of using hydrodynamic simulation endpoints as initial conditions for N-body evolution, revealing that feedback-driven gas removal does not cause rapid expansion as previously thought.

Findings

Simulations with inherited velocities resemble virial equilibrium more than supervirial expansion.

No significant difference between feedback-influenced and non-feedback initial conditions.

Gas removal does not induce rapid expansion beyond dynamical relaxation effects.

Abstract

The removal of gas left over from star formation has long been thought to dominate the dynamical evolution, and dissolution of star-forming regions. Feedback from massive stars from their stellar winds, photoionising radiation and supernovae is postulated to expel significant amounts of gas, altering the gravitational potential energy of the star-forming region and causing a supervirial expansion, which disperses the stars into the Galaxy on rapid timescales (<10Myr). The majority of previous work has utilised N-body simulations with a background potential to model the effects of gas removal. Here, we adopt a different approach where we take the end point of hydrodynamic simulations of star formation in which stars form with and without feedback from massive stars and then evolve the stars as N-body simulations. We also scale the velocities of the stars to various virial ratios, to mimic slower or faster removal of gas, and evolve these as additional N-body simulations. We find that the simulations where the stars inherit the velocities of the sink particles from the hydrodynamic simulations predominantly evolve more like a simulation in virial equilibrium, rather than the supervirial behaviour we would expect after gas removal. We see no significant differences in the dynamical evolution between the simulations where the stars inherit velocities directly from the hydrodynamical simulations and the simulations with (sub)virial velocities. This strongly suggests that gas removal by feedback processes does not lead to rapid expansion of star-forming regions, beyond the expansion caused by dynamical relaxation in star-forming regions.