Structure and Feedback in 30 Doradus II. Structure and Chemical Abundances

TL;DR

This study combines optical imaging, spectroscopy, and photoionization modeling to analyze the physical conditions, structure, and chemical abundances of 30 Doradus, revealing the dominance of X-ray bubbles and limited influence of radiation pressure.

Contribution

It provides detailed, spatially-resolved insights into the structure and feedback processes of 30 Doradus, and validates simplified abundance models against complex observational data.

Findings

X-ray bubbles are in pressure equilibrium and shape the nebula's structure.

Radiation pressure currently has a minor role in nebula shaping.

Simplified strong line models effectively reproduce observed spectra and abundances.

Abstract

We use our new optical-imaging and spectrophotometric survey of key diagnostic emission lines in 30 Doradus, together with CLOUDY photoionization models, to study the physical conditions and ionization mechanisms along over 4000 individual lines of sight at points spread across the face of the extended nebula, out to a projected radius 75 pc from R136 at the center of the ionizing cluster NGC 2070. We focus on the physical conditions, geometry and importance of radiation pressure on a point-by-point basis, with the aim of setting observational constraints on important feedback processes. We find that the dynamics and large scale structure of 30 Dor are set by a confined system of X-ray bubbles in rough pressure equilibrium with each other and with the confining molecular gas. Although the warm (10,000K) gas is photoionized by the massive young stars in NGC 2070, the radiation pressure does not currently play a major role in shaping the overall structure. The completeness of our survey also allows us to create a composite spectrum of 30 Doradus, simulating the observable spectrum of a spatially-unresolved, distant giant extragalactic H II region. We find that the highly simplified models used in the "strong line" abundance technique do in fact reproduce our observed lines strengths and deduced chemical abundances, in spite of the more than one order of magnitude range in the ionization parameter and density of the actual gas in 30 Dor.