Normal galaxy groups contain several optical/NIR luminous galaxies, and are moreover characterized by significant X-ray emission from a hot and dilute IGM at typical temperatures kT=1-2 keV.
Fossil galaxy groups (FGs) have similar X-ray characteristics, but contain only one dominant galaxy (by definition) being at least 2 magnitudes brighter in the R-band than the second brightest group galaxy.
Observations show that 10-20% of all groups are fossil, and the purpose of the work/think-shop was to promote understanding of the fossil group phenomenon, by bringing together a number of specialists in the field.
To guide this process 12 highly sophisticated, cosmological hydro/N-body simulations of the formation and evolution of galaxy groups had been undertaken prior to the work/think-shop. The 12 groups had been selected in an unbiased way from a large, low-resolution cosmological N-body simulation, and rerun at up to 512 times higher mass resolution and 8 times higher force resolution.
The analysis of the simulations was initiated during the workshop, and is now well in progress. Focus is on close comparison to observations, in particular from the small number of FGs known it seems that
During the workshop it was also decided to obtain more observational information about fossil groups - the process is also well in progress.
The results of the work initiated during the workshop will be published in a series of papers, the first of which will be submitted to ApJL in early 2005.
As a first result from the simulation project is shown above the difference between the absolute R-band magnitude of the two brightest galaxies in the groups (at z=0) versus the ratio between the dark matter mass in place within the virial radius at redshifts z=0.5 and z=0:
A very clear correlation is seen indicating that the more "fossil" a galaxy group is the earlier it was assembled.
Jesper Sommer-Larsen and Kristian Pedersen, 3/2-05