Modelling massive-star feedback with Monte Carlo radiation hydrodynamics: photoionization and radiation pressure in a turbulent cloud

TL;DR

This study uses Monte Carlo radiative hydrodynamics to simulate feedback effects of a massive star on a turbulent cloud, revealing efficient gas dispersal, ionization dynamics, and limitations of observational proxies.

Contribution

It introduces a detailed Monte Carlo radiative transfer approach combined with hydrodynamics to model star feedback in turbulent clouds, including synthetic observations.

Findings

All material dispersed within 1.6 Myr or 0.74 free-fall times.

Radiation pressure effects are negligible compared to photoionization.

Dust temperature estimates from continuum ratios can significantly underestimate actual temperatures.

Abstract

We simulate a self-gravitating, turbulent cloud of 1000 Msol with photoionization and radiation pressure feedback from a 34 Msol star. We use a detailed Monte Carlo radiative transfer scheme alongside the hydrodynamics to compute photoionization and thermal equilibrium with dust grains and multiple atomic species. Using these gas temperatures, dust temperatures, and ionization fractions, we produce self-consistent synthetic observations of line and continuum emission. We find that all material is dispersed from the (15.5 pc)$^3$ grid within 1.6 Myr or 0.74 free-fall times. Mass exits with a peak flux of $2 \times 10^{-3}$ Msol/yr, showing efficient gas dispersal. The model without radiation pressure has a slight delay in the breakthrough of ionization, but overall its effects are negligible. 85 per cent of the volume, and 40 per cent of the mass, become ionized -- dense filaments resist ionization and are swept up into spherical cores with pillars that point radially away from the ionizing star. We use free-free emission at 20 cm to estimate the production rate of ionizing photons. This is almost always underestimated: by a factor of a few at early stages, then by orders of magnitude as mass leaves the volume. We also test the ratio of dust continuum surface brightnesses at 450 and 850 micron to probe dust temperatures. This underestimates the actual temperature by more than a factor of 2 in areas of low column density or high line-of-sight temperature dispersion; the HII region cavity is particularly prone to this discrepancy. However, the probe is accurate in dense locations such as filaments.