2003A&A...405.1013R

We investigate interstellar absorption from molecular hydrogen (H₂) and metals in an intermediate-velocity cloud (IVC) in the direction of the LMC star Sk -6880 (HD 36521), based on data from the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. H₂ absorption from the Lyman and Werner bands is detected in 30 lines at radial velocities v_LSR≃+50km/s in this IVC that is presumably located in the Milky Way halo. We obtain a total logarithmic H₂ column density of log N(H₂)=16.6 ±0.5 along with a very low Doppler parameter of b=1.5^+0.8_–0.2km/s. The presence of molecular material in this cloud is suprising, given the fact that the OI column density (logN(OI)=14.8±0.1) implies a very low neutral gas column density of ∼10¹⁸cm^–2 (assuming a solar oxygen abundance). If the H₂ column density represents its abundance in a formation-dissociation equilibrium, the data imply that the molecular gas resides in a small, dense filament at a volume density of ∼800cm^–3 and a thickness of only 41 Astronomical Units (AU). The molecular filament possibly corresponds to the tiny-scale atomic structures (TSAS) in the diffuse interstellar medium observed in high-resolution optical data, HI 21 cm absorption, and in CO emission.