The Cheshire Cat Lens System: The First Case of a Collision Between Fossil Groups?
Abstract
Fossil groups present a puzzle for current theories of structure formation. Despite the paucity of bright galaxies in fossil groups, their high velocity dispersions and high gas temperatures seem to indicate cluster-like gravitational potentials. One extreme example of a potential fossil group(s) is the Cheshire Cat gravitational lens group of galaxies. While it contains two bright central galaxies rather than one (surrounded by 25 galaxies at least two magnitudes fainter), these galaxies are moving at least 1100 km/s relative to one another and might represent the collision of TWO fossil groups. We analyzed data from a moderately long Chandra observation of the Cheshire Cat and found the ICM to have a very hot (6 keV) core, with an X-ray luminosity and M200 value larger than any other known fossil group. Furthermore, the X-ray emission is quite regular, but is not centered on either bright galaxy, but midway between them. We discuss the implications of the Chandra results and whether this system represents the first example of a fossil-group/fossil group merger.
- Publication:
-
AAS/High Energy Astrophysics Division #12
- Pub Date:
- September 2011
- Bibcode:
- 2011HEAD...12.3907I