An Improved Technique for Measurement of Cold HI in Molecular Cloud Cores

Abstract

The presence of atomic gas mixed with molecular species in a "molecular" cloud may significantly affect its chemistry, the excitation of some species, and can serve as probe of the cloud's evolution. Cold neutral atomic hydrogen (HI) in molecular clouds is revealed by its self absorption of background galactic HI 21-cm emission. The properties of this gas can be investigated quantitatively through observation of HI Narrow Self-Absorption (HINSA). In this paper, we present a new technique for measuring atomic gas physical parameters from HINSA observations that utilizes molecular tracers to guide the HINSA extraction. This technique offers a significant improvement in the precision with which HI column densities can be determined over previous methods, and it opens several new avenues of study of relevance to the field of star formation.

arXiv commentAccepted for Astrophycal Journal 8/2008

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• Kinetic tomography of the Galactic plane within 1.25 kiloparsecs from the Sun. The interstellar flows revealed by HI and CO line emission and 3D dust
• Pilot HI Survey of Planck Galactic Cold Clumps with FAST
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• A FAST Survey of HINSA in PGCCs Guided by HC3N
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• Tracing the Formation of Molecular Clouds in a Low-Metallicity Galaxy: A HI Narrow Self-Absorption Survey of the Large Magellanic Cloud
• The evolution of CH in Planck Galactic Cold Clumps
• HI Narrow-Line Self-Absorptions Toward the High-Mass Star-Forming Region G176.51+00.20
• Studies of Molecular Clouds associated with H II Regions: S175
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