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CO and the Multiphase ISM

Published online by Cambridge University Press:  25 May 2016

Christopher F. Mckee
Christopher F. Mckee*
Affiliation:
Departments of Physics and Astronomy, University of California, Berkeley CA 94720

Abstract

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CO observations indicate that molecular clouds have a complex multiphase structure, and this is compared with the multiphase structure of the diffuse interstellar medium. The trace ionization within the molecular gas is governed primarily by UV photoionization. Magnetic fields contribute a significantly larger fraction of the pressure in molecular clouds than in the diffuse interstellar medium. Observations suggest that the total Alfvén Mach number, mAtot, of the turbulence in the diffuse ISM exceeds unity; Zeeman observations are consistent with mAtot ≲ 1 in molecular clouds, but more data are needed to verify this. Most molecular clouds are self-gravitating, and they can be modeled as multi-pressure polytropes with thermal, magnetic, and wave pressure. The pressure and density within self-gravitating clouds is regulated by the pressure in the surrounding diffuse ISM.

Type
Molecular Clouds in the Milky Way
Information
Symposium - International Astronomical Union , Volume 170: CO: Twenty-Five Years of Millimeter-Wave Spectroscopy , 1997 , pp. 25 - 32
Copyright
Copyright © Kluwer 1997 

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