Abstract:
Galaxy groups are important systems in advancing our view of galaxy formation and evolution. Large samples of galaxy groups spanning a wide range of physical parameters will provide a framework to study the properties of galaxy groups. We used (DR7) of SDSS, to extract galaxy groups utilizing modified friend of friends algorithm and we restricted the sample to those with the brightest cluster galaxy (BCG) of brighter than Mr = -22. Next, the luminosity gap, delta_m12 along with a number of parameters for each group including number of galaxies per group and mass is derived for each group. This resulted in an initial sample of 620 groups in which 109 optical fossil groups were also identified following Jones et al. (2003) criteria on delta_m12 . Moreover, semi-analytic model of Bower et al. (2006) has been exploited with 19598 groups with 2060 fossil groups, in a similar manner done for the observational data. In order to investigate the contribution of random processes in forming the statistics, we performed a Monte Carlo simulation of Schechter luminosity function. It has been shown that, fossil BCGs are brighter and live in lower mass halos with respect to their counter parts in non-fossil systems. It has been verified that the brighter absolute magnitude of fossil groups relative to controls in both simulation and observation is mainly contributed by evolutionary processes. Also, luminosity gap in systems with low richness is almost driven by random processes while evolutionary mechanisms are responsible for rich groups. Moreover, in low mass groups also, the luminosity gap is almost caused by random processes while massive halos formed the luminosity gap through evolution.