2005/07/25 by K. Gillmon, Kristen Gillmon, J. Michael Shull · 1 citation
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/498055
published as Astrophys.J.636:908-915,2006 · 22 pages, 8 figures, submitted to ApJ
arxiv created 2005/07/25 · openalex publication_date 2006/01/05 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We combine data from our recent FUSE survey of interstellar molecular hydrogen absorption toward 50 high-latitude AGNs with COBE -corrected IRAS 100 μm emission maps to study the correlation of infrared cirrus with H 2 . A plot of the H 2 column density versus IR cirrus intensity shows the same transition in molecular fraction, f , as seen with total hydrogen column density, N H . This transition is usually attributed to H 2 "self-shielding," and it suggests that many diffuse cirrus clouds contain H 2 in significant fractions, f ≈ 1%-30%. These clouds cover ~50% of the northern sky at b > 30°, at temperature-corrected 100 μm intensities D ≥ 1.5 MJy sr -1 . The sheetlike cirrus clouds, with hydrogen densities n H ≥ 30 cm -3 , may be compressed by dynamical processes at the disk-halo interface, and they are conducive to H 2 formation on grain surfaces. Exploiting the correlation between N and 100 μm intensity, we estimate that cirrus clouds at b > 30° contain ~3000 M ☉ in H 2 . Extrapolated over the inner Milky Way, the cirrus may contain 10 7 M ☉ of H 2 and 10 8 M ☉ in total gas mass. If elevated to 100 pc, their gravitational potential energy is ~10 53 ergs.