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X-ray Observations of Poor Groups

Published online by Cambridge University Press:  12 April 2016

John S. Mulchaey
John S. Mulchaey*
Affiliation:
The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara St., Pasadena, CA91101

Abstract

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X-ray observations of groups have provided considerable new insight into these cosmologically important systems. Recent ROSAT surveys of loose and compact groups suggest that ≃ 50% of all nearby groups contain a hot intragroup medium, including many spiral-rich groups. However, spiral-only groups tend not to be X-ray detected. Spectroscopic studies of X-ray groups indicate that these systems contain a large number of faint galaxies. The existence of a large population of faint galaxies, combined with the extended X-ray halos, is consistent with X-ray detected groups being real, bound systems. The nature of non-X-ray detected groups, which do not contain an extensive faint galaxy population, is still unclear.

ROSAT observations have also revealed the existence of individual elliptical galaxies with X-ray properties and total masses similar to those of X-ray groups. These objects may be the merger remnants of X-ray groups or ‘failed groups’ (i.e. overdensities that formed only a single galaxy). The number density of these objects suggests they make a non-negligible contribution to the mass density of the universe.

Type
Part 2. Properties of Small Groups
Information
International Astronomical Union Colloquium , Volume 174: Small Galaxy Groups , 2000 , pp. 174 - 181
Copyright
Copyright © Astronomical Society of the Pacific 2000

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