Presentation #107.36 in the session “ISM/Galaxies/Clusters (Poster)”.
Fossil Groups (FG) are observationally characterized by a central dominant galaxy that is more than two magnitudes brighter than the second-brightest galaxy in the r-band within half of the R200. They are also brilliant sources of extensive X-ray halo emission (LX,bol > 1042 h-250 erg/s). The origin of fossil groups of galaxies is still very debated. On one hand, the lack of bright galaxies in the vicinity of the BCG suggests that these galaxies were merged by dynamical friction, a process that requires a long time. The higher concentration parameters observed are consistent with very old systems, as predicted by cosmological simulations. On the other hand, they typically lack the very developed cool cores that one would expect for passive, undisturbed systems. In order to investigate how to conciliate these discrepancies, we have raised a representative sample of the fossil groups and fossil group progenitors selecting the best targets from Miller et al. (2012) and Johnson et al. (2018) and obtained HST, Chandra, XMM-Newton, Gemini spectroscopic data for them. Initial analysis from the ICL fraction by mass does show that the systems are older than normal relaxed clusters. The lack of cool cores in these systems is puzzling, especially given the steep central abundance enhancement observed (which is typical of cool core systems). It has been suggested that the hot cores may have been created by shock heating due to a collision with another FG, as in the case of the Cheshire Cat. If that is the case, one would expect the metal enrichment to be similar to that of cool core clusters, presenting a negative radial gradient of the Fe mass fraction from Type Ia SN with respect to core-collapse SN. We here provide the preliminary results for this analysis using the measurements of elemental abundance ratios coupled with the top rank theoretical SN models from Batalha et al. (2022).