What Drives the Expansion of Giant HII Regions?: A Study of Stellar Feedback in 30 Doradus

TL;DR

This study measures various stellar feedback pressures in 30 Doradus, revealing radiation pressure dominates near the core while gas pressure is more significant farther out, informing understanding of HII region expansion.

Contribution

It provides the first detailed observational comparison of different feedback pressures across a giant HII region, clarifying their roles in its expansion.

Findings

Radiation pressure dominates within 75 pc of R136.

HII gas pressure dominates at larger radii.

Hot gas pressure is weak and partially leaks from the shell.

Abstract

Observations show that star formation is an inefficient and slow process. This result can be attributed to the injection of energy and momentum by stars that prevents free-fall collapse of molecular clouds. The mechanism of this stellar feedback is debated theoretically: possible sources of pressure include the classical warm HII gas, the hot gas generated by shock-heating from stellar winds and supernovae, direct radiation of stars, and the dust-processed radiation field trapped inside the HII shell. In this paper, we measure observationally the pressures associated with each component listed above across the giant HII region 30 Doradus in the Large Magellanic Cloud. We exploit high-resolution, multi-wavelengh images (radio, infrared, optical, and X-ray) to map these pressures as a function of position. We find that radiation pressure dominates within 75 pc of the central star cluster, R136, while the HII gas pressure dominates at larger radii. By contrast, the dust-processed radiation pressure and hot gas pressure are generally weak and not dynamically important, although the hot gas pressure may have played a more significant role at early times. Based on the low X-ray gas pressures, we demonstrate that the hot gas is only partially confined and must be leaking out the HII shell. Additionally, we consider the implications of a dominant radiation pressure on the early dynamics of 30 Doradus.