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

We present the detection and analysis of molecular hydrogen emission towards ten interstellar regions in the Large Magellanic Cloud. We examined low-resolution infrared spectral maps of 12 regions obtained with the Spitzer infrared spectrograph (IRS). The pure rotational 0-0 transitions of H₂ at 28.2 and 17.1 μm are detected in the IRS spectra for 10 regions. The higher level transitions are mostly upper limit measurements except for three regions, where a 3s detection threshold is achieved for lines at 12.2 and 8.6 μm. The excitation diagrams of the detected H₂ transitions are used to determine the warm H₂ 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 H₂ gas is found at these temperatures and contributes ~5-17 per cent to the total gas mass. We find a tight correlation of the H₂ surface brightness with polycyclic aromatic hydrocarbon and total infrared emission, which is a clear indication of photoelectric heating in photodissociation regions. We find the excitation of H₂ by this process is equally efficient in both atomic- and molecular-dominated regions. We also present the correlation of the warm H₂ physical conditions with dust properties. The warm H₂ mass fraction and excitation temperature show positive correlations with the average starlight intensity, again supporting H₂ excitation in photodissociation regions.