Chandra and HST Snapshots of Fossil System Progenitors

TL;DR

This study uses Chandra and HST observations to analyze fossil system progenitors, revealing their X-ray properties, galaxy luminosity functions, and evolutionary links to fossil and non-fossil systems.

Contribution

First observational analysis of fossil progenitors with X-ray and optical data, clarifying their evolution and characteristics.

Findings

Progenitors show higher X-ray luminosities and temperatures than expected.

Galaxy luminosity functions support the transition phase hypothesis.

Differences between fossils and non-fossils mainly involve their brightest group galaxies.

Abstract

The search for the progenitors to today's fossil galaxy systems has been restricted to N-body simulations until recently, where 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 in mid brightest group galaxy (BGG) assembly, and all show complex merging environments at their centers. None of these progenitors had archival X-ray data, and many were lacking high resolution optical data making precision photometry extremely difficult. Here, we present Chandra and Hubble Space Telescope (HST) 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 and that fossil systems may themselves be a phase of galaxy system evolution and not a separate class of object.