Fossil groups of galaxies: seeing the future looking at the past

The nature of fossil groups of galaxies has been debated for over more than 3 decades. This is in part because of the lack of deep multiwavelength data and also due to the low purity of samples selected using solely magnitude gap criteria. The initial results of a sample of bonafide fossil groups using X-ray/optical observations has clarified many of their characteristics, such as high central metal abundances and concentration measurements. Recently developed unique ICL markers of the clusters dynamical activity (mergers x relaxed)show very long ages, perhaps having achieved the end of their merging trees. However, they often exhibit hot cores, the nature of which is unknown. We show the comparison of different scenarios to explain the origin and maintenance of the hot cores, based on the analysis of intracluster gas metallicity ratios based on a sample carefully selected bonafide fossil groups and fossil group progenitors by the collaboration MIXDEGS - Multiwavelength ICL & X-ray Detection of Early Galaxy Groups, which include scientists from ON, IAA, MIT, NASA/GSFC, U. Kentucky, U. Alabama, U. W. Alabama, CEA-Saclay, Gemini, STScI and INAF.