Presentation #107.29 in the session “ISM/Galaxies/Clusters (Poster)”.
The origin and evolution of fossil groups (FG) of galaxies are still strongly debated given their contradictory properties when compared to regular groups and clusters. Using a recently found cluster dynamical indicator in the intracluster light fraction (ICLf) color distribution, we apply here an independent age discriminatory test, to a classic FG, RX J1000742.53+380046.6 in combination with new spectroscopic, imaging and X-ray data. We confirm the absence of a cool core, and instead find a negative radial temperature gradient, where the core is about 80% hotter than the outskirts. However, the hot core is also the peak of a strong negative abundance gradient, achieving near solar values. The analysis of the ICLf of the system with HST data does indicate that the system is relaxed, probably more so than all of the CLASH, RELICS and Frontier field clusters where the same analysis has been performed. In particular, the ICLf to mass ratio is significantly higher (by more than 4 times) than any of the clusters previously analysed, which is consistent with an older non-interactive galaxy system that had its last merging event over 3.5 Gyr ago. We discuss the possibility that this system may be the result of FG–FG mergers, similar to that found in the Cheshire Cat system and the implication of this scenario to the survival of FGs throughout their evolutionary history.