Abstract
Numerical simulations as well as optical and Xβray observations over the last few years have shown that poor groups of galaxies can evolve to what is called a fossil group. Dynamical friction as the driving process leads to the coalescence of individual galaxies in ordinary poor groups leaving behind nothing more than a central, massive elliptical galaxy supposed to contain the merger history of the whole group. Due to merging timescales for lessβmassive galaxies and gas cooling timescales of the Xβray intragroup medium exceeding a Hubble time, a surrounding faintβgalaxy population having survived this galactic cannibalism as well as an extended Xβray halo similar to that found in ordinary groups, is expected. Recent studies suggest that fossil groups are very abundant and could be the progenitors of brightest cluster galaxies (BCGs) in the centers of rich galaxy clusters. However, only a few objects are known to the literature. This article aims to summarize the results of observational fossil group research over the last few years and presents ongoing work by the authors. Complementary to previous research, the SDSS and RASS surveys have been crossβcorrelated to identify new fossil structures yielding 34 newly detected fossil group candidates. Observations with ISIS at the 4.2 m William Herschel Telescope on La Palma have been carried out to study the stellar populations of the central ellipticals of 6 fossil groups. In addition multiβobject spectroscopy with VLTs VIMOS has been performed to study the shape of the OLF of one fossil system (Β© 2009 WILEYβVCH Verlag GmbH & Co. KGaA, Weinheim)