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Radio Observations of Giant Extragalactic HII Regions

Published online by Cambridge University Press:  30 March 2016

D. S. Heeschen
D. S. Heeschen*
Affiliation:
National Radio Astronomy Observatory, Charlottesville, Virginia

Extract

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Giant extragalactic HII regions are found in the disks of nearby spiral and irregular galaxies, in the nuclear regions of spiral and elliptical galaxies, and in a variety of peculiar and interacting systems. At radio wavelengths they may emit thermal continuum radiation from the ionized gas and/or nonthermal synchrotron radiation if high energy electrons and magnetic fields are present. In some instances line radiation from associated molecular and neutral hydrogen clouds may also be detected. Table 1 illustrates the sorts of objects in which radio HII regions are observed and indicates the range of radio parameters found. Columns 1 and 2 give the galaxy and specific HII regions within the galaxy. Column 3 is the adopted distance of the galaxy. Column 4 indicates whether the emission is thermal (T) or nonthermal (N-T); column 5 is the 20 cm luminosity, and column 6 the linear size of the radio emitting region. For thermal sources the electron density, derived from the luminosity and size, is listed in column 7. The final column gives references. Note that almost all of the observational information obtainable from radio continuum observations is contained in columns 4, 5, and 6. Very occasionally there may be additional data concerning polarization or variability.

Type
Joint Commission Meetings
Information
Highlights of Astronomy , Volume 6: Highlights of Astronomy. As presented at the XVIIIth General Assembly of the IAU, 1982 , 1983 , pp. 613 - 617
Copyright
Copyright © Reidel 1983

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