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Title:
Diffuse H I Disks in Isolated Galaxies
Authors:
Hogg, David E.; Roberts, Morton S.; Haynes, Martha P.; Maddalena, Ronald J.
Affiliation:
AA(National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under a cooperative agreement with the National Science Foundation ), AB(National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under a cooperative agreement with the National Science Foundation ), AC(Center for Radiophysics and Space Research, Cornell University, Space Sciences Building, Ithaca, NY 14853, USA ; National Astronomy and Ionosphere Center, Cornell University, Space Sciences Building, Ithaca, NY 14853, USA The National Astronomy and Ionosphere Center is operated by Cornell University under a cooperative agreement with the National Science Foundation ), AD(National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24944, USA)
Publication:
The Astronomical Journal, Volume 134, Issue 3, pp. 1046-1060 (2007). (AJ Homepage)
Publication Date:
09/2007
Origin:
IOP
DOI:
10.1086/520766
Bibliographic Code:
2007AJ....134.1046H

Abstract

In order to investigate the contribution of diffuse components to their total H I emission, we have obtained high-precision H I line flux densities with the 100 m Green Bank Telescope for a sample of 100 isolated spiral and irregular galaxies which we have previously observed with the 43 m telescope. A comparison of the observed H I line fluxes obtained with the two different telescopes, characterized by half-power beam widths of 9′ and 21′, respectively, exploits a "beam-matching" technique to yield a statistical determination of the occurrence of diffuse H I components in their disks. A simple model of the H I distribution within a galaxy well describes ~75% of the sample and accounts for all of the H I line flux density. The remaining galaxies are approximately evenly divided into two categories: those which appear to possess a significantly more extensive H I distribution than the model predicts, and those for which the H I distribution is more centrally concentrated than predicted. Examples of both extremes can be found in the literature, but little attention has been paid to the centrally concentrated H I systems. Our sample has demonstrated that galaxies do not commonly possess extended regions of low surface brightness H I gas which is not accounted for by our current understanding of the structure of H I disks. Eight H I-rich companions to the target objects are identified, and a set of extragalactic H I line flux density calibrators is presented.
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