The assembling and environment of clusters of galaxies in the nearby Universe
César Caretta
University of Guanajuato
The nature and evolution of clusters of galaxies have been extensively investigated since the second half of last century. However, since the information available to us is much limited (only projected surface distributions and only line-of-sight velocities, for instance), it is still lacking a complete comprehensive description of their formation and evolution. We have compiled a sample of well observed, in terms of the number of spectroscopic redshifts, nearby clusters of galaxies (z < 0.15) for a deep study of their structure and dynamical properties, trying to compile all the previous information obtained about them. I will present the preliminary results on the study of membership, substructuring and Central Dominant Galaxies (CDGs) for the sample. We found that 55% of the clusters present significant (in terms of relative mass) substructures, one forth of which are multimodal clusters. Concerning to the CDGs, 20% of them are not the 1st. ranked BCM, being this galaxy the CDG of a substructure or a remaining fossil. We also found clusters for which a substructure is more luminous in X-rays than the main cluster structure. The CDGs are continuously distributed in luminosity, confirming that there is no gap between gE and cD galaxies. Large offsets between the position of the CDG and the X-ray centroid are due to the unrelaxed state of the ICM ("cometary-shaped" or multimodal distributions of the hot gas) also related to large central cooling times for these clusters.