Ionizing feedback from massive stars in massive clusters III: Disruption of partially unbound clouds

TL;DR

This study investigates how photoionization from massive stars affects the evolution and disruption of initially unbound star-forming clouds, revealing that cloud mass and initial virial ratio strongly influence feedback effectiveness.

Contribution

It extends previous models to include unbound clouds, showing how ionizing feedback impacts cloud dispersal and star unbinding differently based on initial conditions.

Findings

High-mass clouds are largely unaffected by ionization within 3 Myr.

Lower-mass clouds lose significant gas due to feedback.

Many clouds remain porous to photons and supernova ejecta.

Abstract

We extend our previous SPH parameter study of the effects of photoionization from O-stars on star-forming clouds to include initially unbound clouds. We generate a set of model clouds in the mass range $10^{4}-10^{6}$M$_{\odot}$ with initial virial ratios $E_{\rm kin}/E_{\rm pot}$=2.3, allow them to form stars, and study the impact of the photoionizing radiation produced by the massive stars. We find that, on the 3Myr timescale before supernovae are expected to begin detonating, the fractions of mass expelled by ionizing feedback is a very strong function of the cloud escape velocities. High-mass clouds are largely unaffected dynamically, while lower-mass clouds have large fractions of their gas reserves expelled on this timescale. However, the fractions of stellar mass unbound are modest and significant portions of the unbound stars are so only because the clouds themselves are initially partially unbound. We find that ionization is much more able to create well-cleared bubbles in the unbound clouds, owing to their intrinsic expansion, but that the presence of such bubbles does not necessarily indicate that a given cloud has been strongly influenced by feedback. We also find, in common with the bound clouds from our earlier work, that many of the systems simulated here are highly porous to photons and supernova ejecta, and that most of them will likely survive their first supernova explosions.