PI: Mischa Schirmer, Gemini Observatory, firstname.lastname@example.org
Address: Southern Operations Centre, Casilla 603, La Serena, Chile
CoI: Sherry Suyu, University of California
CoI: Rodrigo Carrasco, Gemini Observatory
CoI: Karianne Holhjem, SOAR telescope
Title: Determining the redshift of the strong lens system in the fossil group J0454-0309
Abstract: Fossil groups of galaxies exhibit very bright elliptical galaxies, embedded in a diffuse X-ray halo, and form potential seeds for the brightest cluster galaxies (BCGs). These groups are thought to represent the last stage of mass assembly in the Universe. Only a few dozen fossil systems are known to date, and only one of them, J0454- 0309, features a strongly lensed gravitational arc. We have argued in Schirmer et al. (2010) that the lensing geometry of this system implies that its giant elliptical does not lie at the center of the group's gravitational potential. This contradicts current theories of structure formation. The only possible explanation is an infall scenario, where the elliptical formed outside and is now infalling into a sparse cluster, or that galaxies in a filament stream along the line of sight onto the fossil group. To confirm that the offset is indeed real (and thus the infall scenario), we must confirm the nature of the lensed counter image and prove the arc to be at high redshift.
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