2005/12/16 by B. P. Wakker · 1 citation
Physics and Astronomy · #astro-ph
paper · pdf · doi:10.1086/500365
Accepted for ApJ Supplement. Note: figs 7 and 8 not included because astro-ph rejects them as too big
arxiv created 2005/12/16 · arxiv updated 2009/12/01
Measurements of molecular hydrogen (H2) column densities are presented for the first six rotational levels (J=0 to 5) for 73 extragalactic targets observed with FUSE. All of these have a final signal-to-noise ratio larger than \snlimit, and are located at galactic latitude |b|>20 deg. The individual observations were calibrated with the FUSE calibration pipeline CalFUSE version 2.1 or higher, and then carefully aligned in velocity. The final velocity shifts for all the FUSE segments are listed. H2 column densities or limits are determined for the 6 lowest rotational (J) levels for each HI component in the line of sight, using a curve-of-growth approach at low column densities ~16.5), and Voigt-profile fitting at higher column densities. Detections include 73 measurements of low-velocity H2 in the Galactic Disk and lower Halo. Eight sightlines yield non-detections for Galactic H2. The measured column densities range from log N(H2)=14 to log N(H2)=20. Strong correlations are found between log N(H2) and T01, the excitation temperature of the H2, as well as between log N(H2) and the level population ratios (log (N(J')/N(J))). The average fraction of nuclei in molecular hydrogen (f(H2)) in each sightline is calculated; however, because there are many HI clouds in each sightline, the physics of the transition from HI to H2 can not be studied. Detections also include H2 in 16 intermediate-velocity clouds in the Galactic Halo (out of 35 IVCs). Molecular hydrogen is seen in one high-velocity cloud (the Leading Arm of the Magellanic Stream), although 19 high-velocity clouds are intersected; this strongly suggests that dust is rare or absent in these objects. Finally, there are five detections of H2 in external galaxies.