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Ionised Hydrogen at Large Galactocentric Distances

Published online by Cambridge University Press:  05 March 2013

J. Bland-Hawthorn
J. Bland-Hawthorn*
Affiliation:
Anglo-Australian Observatory, PO Box 296, Epping, NSW 2121, Australia; jbh@aaossz.aao.gov.au
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Abstract

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We summarise recent attempts to detect warm ionised gas at large galactocentric distances. This includes searches for gas at the edges of spirals, in between cluster galaxies, towards extragalactic HI clouds, and towards high-velocity clouds and the Magellanic Stream in the Galaxy. With the exception of extragalactic HI clouds, all of these experiments have proved successful. Within each class, we have only observed a handful of objects. It is premature to assess what fraction of the missing baryonic mass fraction might be in the form of ionised gas. But, in most cases, the detections provide a useful constraint on the ambient ionising flux, and, in the case of spiral edges, can even trace dark matter haloes out to radii beyond the reach of radio telescopes.

Keywords

galaxies: kinematics and dynamicsdark matter: cosmic radiation field: galactic radiation field
Type
Research Article
Information
Publications of the Astronomical Society of Australia , Volume 14 , Issue 1 , 1997 , pp. 64 - 68
Copyright
Copyright © Astronomical Society of Australia 1997

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