Unveiling the Nature of Fossil Groups with XMM-HST II\: Reducing Variance

Fossil groups (FGs) present a puzzle to theories of structure formation. Despitethe low number of bright galaxies, their high velocity dispersions and high T_Xseem to indicate clusterlike potential wells. Their measured c200 are highindicating early formation epochs, in contradiction with the observed lack ofexpected large cool cores. We have proposed a discriminatory test, using theintracluster light to mass ratio (ICLf/M) in FGs, using XMM and HST. The pilotstudy was successful and suggests that FGs are not merging and show high ICLf/Mratios in comparison to relaxed systems. We propose to increase the sample ofbonafide FGs complementing XMM and HST archived observations to account forsample variance, allowing us to reliably constrain their formation mechanisms and ages. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]