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The Search for Cold Molecular Gas in the Outer Galaxy

Published online by Cambridge University Press:  25 May 2016

E.J. de Geus  and
J.A. Phillips
E.J. de Geus
Affiliation:
Caltech MS 105-24, Pasadena, CA 91125, USA
J.A. Phillips
Affiliation:
Caltech MS 105-24, Pasadena, CA 91125, USA

Extract

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It is well known that the rotation curves of many galaxies remain flat well outside their optical disks. This leads to the conclusion that the visible mass in galaxies is only a small fraction of the total (see e.g. Faber & Gallagher 1979). Although we are certain that “dark matter” exists, its composition and distribution are still unknown.

In a recent paper Pfenniger et al. (1994) argued strongly for the possibility that dark matter could well be in the form of cold, predominantly molecular gas in a flat distribution. To have escaped previous detection in the outer parts of our Galaxy, the gas would need to have a low temperature and thus a low emissivity. Because most substantial heating sources of gas are associated with the presence of massive stars (UV radiation and cosmic rays) this requirement may be satisfied in the Galactic plane outside the optical disk.

Type
Chapter 7: How are we to Understand the Small Scale Structure of the ISM?
Information
Symposium - International Astronomical Union , Volume 169: Unsolved Problems of the Milky Way , 1996 , pp. 575 - 582
Copyright
Copyright © Kluwer 1996 

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