Fossil groups are systems with masses and X-ray luminosities comparable to those of groups and clusters of galaxies, but whose light is dominated by a single, isolated, large elliptical galaxy. Their denomination, “fossil”, comes from their possible formation scenario in which they may have collapsed at an early epoch, being the oldest and most undisturbed galaxy systems not yet absorbed by larger halos.

Studies of fossil groups have started fairly recently — the first such group was identified by Ponman et al. (1994). Two articles performed searches for such systems using well defined selection criteria (Vikhilinin et al. 1999 and Jones et al. 2003) and concluded that they are very abundant — their density is ~2.4 x 10^-7 Mpc^-3 (Jones et al. 2003). There are, however, only 15 fossil groups known in the literature (Table 4 of Mendes de Oliveira et al. 2006) and a few more have been catalogued since then. The main contribution of this work is to present a new list of fossil groups, obtained from a search in the SDSS-DR5 (Adelman-McCarthy et al. 2007) database.

Note that the work described here will be presented as a scientific article (Santos et al. 2007), with far more scientific discussion on the method (including other parameter values for the search) and especially on the results. Here, instead, we focus on the technical procedures of the work.