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Cold H I in turbulent eddies and galactic spiral shocks

Published online by Cambridge University Press:  01 August 2006

Steven J. Gibson ,
A. Russell Taylor ,
Jeroen M. Stil ,
Christopher M. Brunt ,
Dain W. Kavars  and
John M. Dickey
Steven J. Gibson
Affiliation:
Arecibo Observatory, National Astronomy and Ionosphere Center, Arecibo, PR 00612, U.S.A.
A. Russell Taylor
Affiliation:
Dept. of Physics & Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada
Jeroen M. Stil
Affiliation:
Dept. of Physics & Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada
Christopher M. Brunt
Affiliation:
School of Physics, University of Exeter, Exeter, United KingdomEX4 4QL
Dain W. Kavars
Affiliation:
Department of Astronomy, University of Minnesota, Minneapolis, MN 55455, U.S.A.
John M. Dickey
Affiliation:
Department of Astronomy, University of Minnesota, Minneapolis, MN 55455, U.S.A. School of Mathematics and Physics, University of Tasmania, Hobart, TAS 7001, Australia
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Abstract

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H I 21cm-line self-absorption (HISA) reveals the shape and distribution of cold atomic clouds in the Galactic disk. Many of these clouds lack corresponding CO emission, despite being colder than purely atomic gas in equilibrium models. HISA requires background line emission at the same velocity, hence mechanisms that can produce such backgrounds. Weak, small-scale, and widespread absorption is likely to arise from turbulent eddies, while strong, large-scale absorption appears organized in cloud complexes along spiral arm shocks. In the latter, the gas may be evolving from an atomic to a molecular state prior to star formation, which would account for the incomplete HISA-CO agreement.

Keywords

radiative transfersurveysISM: cloudsISM: evolutionISM: kinematics and dynamicsISM: structureGalaxy: structureradio lines: ISM
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S237: Triggered Star Formation in a Turbulent ISM , August 2006 , pp. 363 - 367
Copyright
Copyright © International Astronomical Union 2007

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