Rotationally Excited H2 in the Magellanic Clouds

We have performed a survey study of rotational excited-state H₂ Lyman-Werner absorption lines in the entire FUSE Magellanic Clouds Legacy archive. These lines reflect the UV pumping and formation conditions of H₂, enabling a more comprehensive study of H₂ gas properties, e.g. J-level populations N(J) and b-values (generally indicating the velocity dispersion). Combining with our previous measurements of N(Hi) and N(H₂), we derived H₂ excitation temperatures, gas volume density n(H), and local UV radiation field strength I _UV for each sight line. The results indicate a weaker correlation between n(H) and I _UV in Magellanic Clouds than the Galactic sight lines. We also obtained N(H)/E(B - V) ratios from the Spitzer-SAGE and previous CO J = 1 - 0 / Hi 21 cm surveys at sight line locations, using dust modeling and standard line brightness-column density conversion factors. They show a roughly linear correlation with absorption-based N(H)/E(B - V) values, and have a similar scatter (∼0.7 dex) across the LMC and SMC.