Volume 405, Number 3, July III 2003
|Page(s)||1013 - 1023|
|Section||Interstellar and circumstellar matter|
|Published online||30 June 2003|
H2 absorption in a dense interstellar filament in the Milky Way halo
Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
2 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
3 Center for Astrophysics & Space Sciences, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093, USA
Corresponding author: P. Richter, email@example.com
Accepted: 12 May 2003
We investigate interstellar absorption from molecular hydrogen (H2) and metals in an intermediate-velocity cloud (IVC) in the direction of the LMC star Sk -68 80 (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 km s-1 in this IVC that is presumably located in the Milky Way halo. We obtain a total logarithmic H2 column density of log H along with a very low Doppler parameter of km s-1. The presence of molecular material in this cloud is suprising, given the fact that the O i column density (log O i) implies a very low neutral gas column density of cm-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 ∼800 cm-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, H i 21 cm absorption, and in CO emission.
Key words: Galaxy: halo / ISM: molecules / ISM: structure
© ESO, 2003
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