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High-Density, Cool Regions of Interstellar Matter in the Galaxy

Published online by Cambridge University Press:  14 August 2015

W. B. Burton  and
H. S. Liszt
W. B. Burton
Affiliation:
Department of Astronomy, University of Minnesota
H. S. Liszt
Affiliation:
National Radio Astronomy Observatory

Extract

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The distribution of interstellar nucleons is dominated by gas at temperatures ranging from a few K to a few hundred K. At the warmer end of this temperature range, the gas is predominantly in the form of ubiquitously distributed atomic hydrogen. The colder gas is almost entirely molecular; it resides in compressed clumps, confined principally to the inner-galaxy, and is most effectively traced by observations of carbon monoxide. In this paper, we focus on some of the problems which currently hinder derivation of the morphology and total number of nucleons in the galaxy. For the atomic gas, these problems involve optical depth effects in HI profiles, the amount of cold HI residing in molecular clouds, and the form of the outer-galaxy rotation curve. For the molecular gas, the problems involve the uncertainties in the conversion from CO intensities to H2 densities, including the possibility of composition gradients across the galaxy, the total number and typical size of molecular clouds, and the possibility that the molecular material in the region of the galactic nucleus is distributed differently from the material in the galaxy at large.

Type
Research Article
Information
Symposium - International Astronomical Union , Volume 94: Origin of Cosmic Rays , 1981 , pp. 227 - 250
Copyright
Copyright © Reidel 1981 

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