The Properties of Fossil Groups of Galaxies
  Numerical simulations as well as optical and X-ray 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 less-massive
galaxies and gas cooling timescales of the X-ray intragroup medium exceeding a
Hubble time, a surrounding faint-galaxy population having survived this
galactic cannibalism as well as an extended X-ray 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 cross-correlated to identify new fossil structures yielding 34 newly
detected fossil group candidates. Observations with ISIS at the 4.2m 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
multi-object spectroscopy with VLTs VIMOS has been performed to study the shape
of the OLF of one fossil system.
