Program: GN-2020A-Q-317

Fossil groups of galaxies (FG) present a puzzle to theories of structure formation. Their lack of bright central galaxies and the high measured concentration parameters indicate early formation epochs, in contradiction with the observed lack of expected large cool cores seen in X-rays. We developed a new discriminatory test to assess the relative age of these systems, using measurements of the intracluster light in combination with the system’s mass. We applied it to a classic fossil group, RX J100742+380046, together with granted XMM, HST and Gemini data and obtained tantalizing results. To complete the pilot study for FGs we need accurate measurements of the system’s light and for that we need to remove of fore/background galaxies, especially for systems with low density of galaxies such as FGs. To address that, we propose here a short observational program to obtain the necessary redshifts for the visible targets of our carefully selected sample to corroborate the preliminary results and take the project to its full completion.