The Dynamics of Radiation Pressure-Dominated HII Regions

TL;DR

This paper investigates the significance of radiation pressure in the expansion and dynamics of HII regions, highlighting its dominance in large, cluster-driven regions and its role in star formation regulation.

Contribution

It provides a criterion for when radiation pressure dominates HII region dynamics and offers a solution for their expansion under radiation pressure influence.

Findings

Radiation pressure is negligible in small HII regions driven by few stars.

Radiation pressure dominates in large, cluster-driven HII regions.

HII regions likely regulate the formation of massive star clusters.

Abstract

We evaluate the role of radiation pressure in the dynamics of HII regions. We first determine under what conditions radiation pressure is significant in comparison to gas pressure and show that, while radiation pressure is generally unimportant for HII regions driven by a handful of massive stars, it is dominant for the larger HII regions produced by the massive star clusters found near the Galactic center and in starburst environments. We then provide a solution for the problem of how HII regions expand when radiation pressure influences their behavior. Finally, we compare radiation-dominated HII regions to other sources of stellar feedback, and argue that HII regions are probably the primary mechanism for regulating the formation of massive star clusters.