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2003MNRAS.343..627J - Mon. Not. R. Astron. Soc., 343, 627-638 (2003/August-1)
The nature and space density of fossil groups of galaxies.
JONES L.R., PONMAN T.J., HORTON A., BABUL A., EBELING H. and BURKE D.J.
Abstract (from CDS):
The characteristic feature of the fossil groups we study is that most of the light arises from one dominant, central galaxy. We define a fossil system and, based on this definition, construct a small X-ray-selected, flux-limited sample of fossil groups with well-known selection criteria. We confirm that these systems are indeed groups of galaxies, but dominated by one central luminous giant elliptical galaxy and with few, or no, L * galaxies. We find that fossil systems represent 8-20 per cent of all systems of the same X-ray luminosity. Fossil groups are at least as numerous as all poor and rich clusters combined, and are thus a possible site for the formation of luminous central cluster galaxies before infall into clusters occurs. The fossil systems in our sample have significantly higher X-ray luminosities than normal groups of similar total optical luminosities (or similar X-ray temperature, where the latter can be measured). These enhanced X-ray luminosities may be due to relatively cool gas in the innermost regions or due to a low central gas entropy. We interpret fossil groups as old, undisturbed systems which have avoided infall into clusters, but where galaxy merging of most of the L * galaxies has occurred. An early formation epoch, before that of most groups, could explain low central gas entropies and high X-ray luminosities.
Abstract Copyright: 2003 RAS
Journal keyword(s): galaxies: clusters: general - galaxies: elliptical and lenticular, cD - galaxies: general - X-rays: galaxies: clusters
Simbad objects: 9
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