2000ApJ...538L..73S

We describe a moderate-resolution Far Ultraviolet Spectroscopic Explorer (FUSE) minisurvey of H₂ in the Milky Way and Magellanic Clouds using four hot stars and four active galactic nuclei as background sources. FUSE spectra of nearly every stellar and extragalactic source exhibit numerous absorption lines from the H₂ Lyman and Werner bands between 912 and 1120 Å. One extragalactic sight line (PKS 2155-304) with low N(H I) shows no detectable H₂ and could be the ``Lockman Hole of molecular gas'', of importance for QSO absorption-line studies. We measure H₂ column densities in low rotational states (J=0 and 1) to derive rotational and/or kinetic temperatures of diffuse interstellar gas. The higher J abundances can constrain models of the UV radiation fields and gas densities. In three optically thick clouds toward extragalactic sources, we find n_H~30-50 cm^–3 and cloud thicknesses ∼2-3 pc. The rotational temperatures for H₂ at high Galactic latitude, <T₀₁≥107±17 K (seven sight lines) and 120±13 K (three optically thick clouds), are higher than those in the Copernicus sample composed primarily of targets in the disk. We find no evidence for great differences in the abundance or state of excitation of H₂ between sight lines in the Galaxy and those in the SMC and LMC. In the future, we will probe the distribution and physical parameters of diffuse molecular gas in the disk and halo and in the lower metallicity environs of the LMC and SMC.