A survey of H I narrow self-absorption in molecular cores.
KRCO M. and GOLDSMITH P.F.
Abstract (from CDS):
The study of cold atomic hydrogen (H I) in molecular clouds has the potential to significantly improve our understanding of the formation of molecular clouds, the atomic to molecular hydrogen conversion process, and star formation. Result. from the first large survey of H I Narrow Self Absorption (HINSA) features outside of the Taurus Molecular Cloud Complex are presented. Previous hypotheses that cold atomic hydrogen represents the third largest constituent of molecular clouds are confirmed with a mean abundance of 10–2.8 in comparison with the total proton column density. HINSA features are observed in over 80% of the observed clouds, accompanied by indications that cold H I probably exists in all clouds. We find that HINSA features are observable to distances of at least 700 pc. Nine clouds have been mapped in detail revealing that HINSA abundances can vary significantly within a cloud both spatially and in an individual velocity component. Possible explanations for this phenomenon are briefly discussed.