paper

Molecular hydrogen emission in the interstellar medium of the Large Magellanic Cloud

arXiv:1407.7658 · doi:10.1093/mnras/stu2276

Abstract

We present the detection and analysis of molecular hydrogen emission toward ten interstellar regions in the Large Magellanic Cloud. We examined low-resolution infrared spectral maps of twelve regions obtained with the Spitzer infrared spectrograph (IRS). The pure rotational 0--0 transitions of H $_{2}$ at 28.2 and 17.1 $I^¼ m$ are detected in the IRS spectra for ten regions. The higher level transitions are mostly upper limit measurements except for three regions, where a 3 $I ¨ $ detection threshold is achieved for lines at 12.2 and 8.6 $I^¼ m$ . The excitation diagrams of the detected H $_{2}$ transitions are used to determine the warm H $_{2}$ gas column density and temperature. The single-temperature fits through the lower transition lines give temperatures in the range $86 - 137 K$ . The bulk of the excited H $_{2}$ gas is found at these temperatures and contributes $\sim$ 5-17% to the total gas mass. We find a tight correlation of the H $_{2}$ surface brightness with polycyclic aromatic hydrocarbon and total infrared emission, which is a clear indication of photo-electric heating in photodissociation regions. We find the excitation of H $_{2}$ by this process is equally efficient in both atomic and molecular dominated regions. We also present the correlation of the warm H $_{2}$ physical conditions with dust properties. The warm H $_{2}$ mass fraction and excitation temperature show positive correlations with the average starlight intensity, again supporting H $_{2}$ excitation in photodissociation regions.

Accepted for publication in MNRAS