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Density Bounding of Giant HII Regions and the Ionisation of the Diffuse Interstellar Medium

Published online by Cambridge University Press:  05 March 2013

J. E. Beckman*
Affiliation:
Instituto de Astrofísica de Canarias, La Laguna 38200, Spain
M. Rozas
Affiliation:
Instituto de Astrofísica de Canarias, La Laguna 38200, Spain
J. H. Knapen
Affiliation:
Department of Physics, University of Herfordshire, College Lane, Herts. A21D 9AB, UK
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Abstract

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Three different types of evidence are presented in favour of the hypothesis that the HII regions in disk galaxies with Hα luminosities greater than a critical value of 1038·6 erg s−1 are density-bounded, and that the escaping Lyman continuum photons from these are the principal ionising agents for the diffuse ISM in disk galaxies. This has important implications for the ionisation of the intergalactic medium, and for computed star formation rates in spirals.

Type
Research Article
Copyright
Copyright © Astronomical Society of Australia 1998

References

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