Dr. Omar López Cruz.
Instituto Nacional de Astrofísica, Óptica y Electrónica, Tonantzinltla, Puebla.

Fossil groups exhibit extended X-ray halos similar to those in poor clusters; however, in the optical they show a dominant luminous elliptical galaxy surrounded by fainter companions, tantamount to Bautz-Morgan I, I-II clusters. As anticipated in dynamical studies and high resolution numerical simulations, it has been suggested that fósil groups could be the end-product of the collapse of dense groups or poor clusters. We have cross-matched the SDSS and the ROSAT All-Sky Survey to search for fossil groups using National Virtual Observatory (NVO) technologies (e.g., OpenSkyQuery & SkyView).

We have found a large number of fossil groups candidates, some of them have been included in a XMM-Newton observing proposal, in order to analyze in more detail the extended X-ray emission. We present preliminary results based on the analysis of archival data.