Are fossil groups a challenge of the CDM paradigmquestionMark

Fossil groups may have up to two orders of magnitude less substructure thanpredicted in CDM simulations. The significance of this lack of substructuredepends on the depth of the galaxy luminosity function and on the mass of thegroup. We have initiated a project to determine the substructure distributionfunction (SDF) for the members of a representative sample of 4 REFLEX fossilgroups down to M^* + 6 within a large fraction of the infall region. We willobtain Xray observations of two fossil groups to complete the Xray sample, tocomplement the optical observations and to compare with new simulations. We willcompare the SDF from optical and Xray mass estimates with theoreticalpredictions. We will establish if fossil groups do challenge the CDM paradigm. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]