Chandra and HST Snapshots of Fossil System Progenitors

The search for the progenitors to today's fossil galaxy systems has been restricted to N-body simulations until recently, when 12 fossil progenitors were identified in the CASSOWARY catalog of strong-lensing systems. All 12 systems lie in the predicted redshift range for finding fossils that are in the process of assembling their brightest group galaxy (BGG), and all show complex merging-like environments at their centers. Here, we present Chandra and Hubble Space Telescope snapshots of eight of these strong-lensing fossil progenitors at varying stages of evolution. We find that our lensing progenitors exhibit higher than expected X-ray luminosities and temperatures consistent with previously observed non-lensing fossil systems. More precise galaxy luminosity functions are generated, which strengthen past claims that progenitors are the transition phase between non-fossils and fossils. We also find evidence suggesting that the majority of differences between fossils and non-fossils lie in their BGGs.