Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21531902k&link_type=abstract
American Astronomical Society, AAS Meeting #215, #319.02; Bulletin of the American Astronomical Society, Vol. 42, p.320
Astronomy and Astrophysics
Astronomy
Scientific paper
We present the results of a survey of 48 molecular cloud cores and a large map covering over 100 square degrees of the Taurus Molecular Cloud Complex in cold HI absorption as well as 12CO and 13CO emission. Using a new technique developed for detecting and analyzing HI Narrow Self-Absorption (HINSA) features caused by cold HI gas within molecular clouds, this study presents a significantly more detailed examination of the HI to H2 ratio in molecular clouds than previously available. It represents an important step toward our understanding of the atomic to molecular gas conversion process in dense clouds which will become star forming regions. Our study shows that probably all molecular clouds contain at least the steady-state abundance of cold HI produced by cosmic-ray dissociation of H2 ( 2 cm-3), and that this gas is detectable to a distance of at least 700pc. Typical HI column densities are of order (1019 cm-2) and HI/H2 column density ratios range from 10-3 to 10-5. Many clouds exhibit HI abundances significantly above expected steady-state levels, which is indicative of possible ongoing chemical evolution. We show that many molecular clouds, including the Taurus Molecular Cloud complex, exhibit variations in their atomic to molecular gas ratios, even at similar volume densities, both as a function of sky position but also among different velocity components along a single line of sight.
Goldsmith Paul F.
Krco Marko
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