Massive stars in massive clusters II: Disruption of bound clusters by photoionization

TL;DR

This study uses SPH simulations to analyze how photoionization from massive stars affects star-forming clouds of different masses, showing that feedback significantly disrupts lower-mass clouds but not the most massive ones.

Contribution

It provides a detailed parameter study demonstrating the varying impact of photoionization feedback on clouds of different masses and densities before supernovae occur.

Findings

Lower-density clouds are heavily disrupted by ionizing feedback.

Massive clouds (>10^6 M_sun) are largely unaffected due to high escape velocities.

Ionization creates large evacuated bubbles in less massive clouds.

Abstract

We present an SPH parameter study of the dynamical effect of photoionization from O--type stars on star--forming clouds of a range of masses and sizes during the time window before supernovae explode. Our model clouds all have the same degree of turbulent support initially, the ratio of turbulent kinetic energy to gravitational potential energy being set to $E_{\rm kin}/|E_{\rm pot}|$=0.7. We allow the clouds to form stars and study the dynamical effects of the ionizing radiation from the massive stars or clusters born within them. We find that dense filamentary structures and accretion flows limit the quantities of gas that can be ionized, particularly in the higher density clusters. More importantly, the higher escape velocities in our more massive (10$^{6}$M$_{\odot}$) clouds prevent the HII regions from sweeping up and expelling significant quantities of gas, so that the most massive clouds are largely dynamically unaffected by ionizing feedback. However, feedback has a profound effect on the lower--density 10$^{4}$ and 10$^{5}$M$_{\odot}$ clouds in our study, creating vast evacuated bubbles and expelling tens of percent of the neutral gas in the 3Myr timescale before the first supernovae are expected to detonate, resulting in clouds highly porous to both photons and supernova ejecta.