Molecular and Ionized Hydrogen in 30 Doradus. I. Imaging Observations

TL;DR

This study provides the first calibrated imaging of molecular hydrogen in 30 Doradus, revealing the morphology and excitation mechanisms of the warm molecular gas and its relation to ionized regions.

Contribution

It presents the first fully calibrated H$_2$ imaging of 30 Doradus, analyzing the morphology and excitation of molecular hydrogen in relation to other emissions.

Findings

H$_2$ emission is from photodissociation regions near the ionization front.

H$_2$ emission is primarily due to fluorescence, not shocks.

The environment has a density less than 10^4 cm$^{-3}$.

Abstract

We present the first fully calibrated H$_2$, 1-0 S(1) image of the entire 30 Doradus nebula. The observations were conducted using the NOAO Extremely Wide-Field Infrared Imager on the CTIO 4-meter Blanco Telescope. Together with a NEWFIRM Br$\gamma$ image of 30 Doradus, our data reveal the morphologies of the warm molecular gas and ionized gas in 30 Doradus. The brightest H$_2$-emitting area, which extends from the northeast to the southwest of R136, is a photodissociation region viewed face-on, while many clumps and pillar features located at the outer shells of 30 Doradus are photodissociation regions viewed edge-on. Based on the morphologies of H$_2$, Br$\gamma$, $^{12}$CO, and 8$\mu$m emission, the H$_2$ to Br$\gamma$ line ratio and Cloudy models, we find that the H$_2$ emission is formed inside the photodissociation regions of 30 Doradus, 2 - 3 pc to the ionization front of the HII region, in a relatively low-density environment $<$ 10$^4$ cm$^{-3}$. Comparisons with Br$\gamma$, 8$\mu$m, and CO emission indicate that H$_2$ emission is due to fluorescence, and provide no evidence for shock excited emission of this line.