Measuring the Atomic to Molecular Gas Ratio in Molecular Cloud Cores

Details Measuring the Atomic to Molecular Gas Ratio in Molecular Cloud Cores Measuring the Atomic to Molecular Gas Ratio in Molecular Cloud Cores

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21348509k&link_type=abstract

American Astronomical Society, AAS Meeting #213, #485.09; Bulletin of the American Astronomical Society, Vol. 41, p.457

Astronomy and Astrophysics

Astronomy

1

Scientific paper

HI Narrow Self-Absorption (HINSA) is a 21cm absorption feature which is caused by cold HI gas in the well-shielded interiors of molecular clouds and dense cloud cores. A survey using the Green Bank Telescope (GBT) of over 70 molecular cloud cores with distances of up to 700pc has found that nearly half of them exhibit HINSA features. This HI gas may be a remnant of the HI-H2 conversion process which occurs during the collapse of a diffuse atomic hydrogen cloud to form a dense molecular cloud. Comparison with 13CO emission obtained with the Five College Radio Astronomy Observatory (FCRAO) 14 m telescope yields HI/H2 ratios for over 30 molecular cloud cores. New techniques allow for more accurate determination of the HINSA content of individual velocity components within a cloud. As a result we are now able to estimate the chemical ages of molecular cloud cores and their individual components by determining their HI/H2 ratios. We find that while some clouds exhibit similar chemical ages for all their components, other clouds seem to have different ages for components along the same line of sight.

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