# The effect of the virial state of molecular clouds on the influence of feedback from massive stars

## TL;DR

This study uses SPH simulations to examine how the virial state of molecular clouds affects feedback from massive stars, revealing modest reductions in star formation efficiency and significant unbinding of material, primarily driven by momentum transfer rather than thermal expansion.

## Contribution

It demonstrates that feedback effects can be effectively modeled as steady momentum injection, highlighting the role of virial ratios and escape velocities in feedback efficiency.

## Key findings

- Star formation efficiency reduced by 30-50% due to feedback.
- Unbound material ranges from 20-60%, especially in low escape velocity clouds.
- Feedback effects are mainly due to momentum transfer, not thermal expansion.

## Abstract

A set of Smoothed Particle Hydrodynamics simulations of the influence of photoionising radiation and stellar winds on a series of 10$^{4}$M$_{\odot}$ turbulent molecular clouds with initial virial ratios of 0.7, 1.1, 1.5, 1.9 and 2.3 and initial mean densities of 136, 1135 and 9096\,cm$^{-3}$ are presented. Reductions in star formation efficiency rates are found to be modest, in the range $30\%-50\%$ and to not vary greatly across the parameter space. In no case was star formation entirely terminated over the $\approx3$\,Myr duration of the simulations. The fractions of material unbound by feedback are in the range $20-60\%$, clouds with the lowest escape velocities being the most strongly affected.\\ Leakage of ionised gas leads to the HII regions rapidly becoming underpressured. The destructive effects of ionisation are thus largely not due to thermally--driven expansion of the HII regions, but to momentum transfer by photoevaporation of fresh material. Our simulations have similar global ionisation rates and we show that the effects of feedback upon them can be adequately modelled as a steady injection of momentum, resembling a momentum--conserving wind.