Oct 17, 2012

Rui Xue, University of Illinois at Urbana-Champaign

"Interstellar HI and H2 in the Magellanic Clouds"

We have determined column densities of HI and/or H2 for sight lines in the Magellanic Clouds from archival Hubble Space Telescope and Far-Ultraviolet Spectroscopic Explorer spectra of HI Lyα and H2 Lyman-band absorption. Together with some similar data from the literature, we now have absorption-based N(HI) and/or N(H2) for 285 Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) sight lines (114 with a detection or limit for both species). For the same sample, we are performing a survey study of rotational excited-state H2 Lyman-Werner absorption lines, which reflect the UV pumping and formation conditions of H2, enabling a more comprehensive study of H2 gas properties (e.g. J-levels populations) and local UV radiation fields. I will report results on the molecular fractions and gas-to-dust ratios from our absorption measurements, in these two nearby low-metallicity galaxies. In addition, comparisons of emission/absorption-based interstellar gas and dust properties at sight line locations will be presented.