Molecular hydrogen emission in the interstellar medium of the Large
  Magellanic Cloud
  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${\,\rm \mu m}$ 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$\sigma$ detection threshold is achieved for
lines at 12.2 and 8.6${\,\rm \mu m}$. 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 $86-137\,{\rm K}$. 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.
