A study of the core of the Shapley Concentration: V. The A3528 complex: a young merger event?

We present the results of a redshift survey of galaxies in the A3528 complex, a chain of interacting clusters in the core of the Shapley Concentration. This complex is characterized in the X-ray band by two pairs of roughly similar interacting clumps: one pair has been resolved as two optical Abell clusters (A3530 and A3532), while the two components of the other pair are both associated to A3528. The optical data show that the distance between the centers of A3530 and A3532 is smaller than their Abell radii, an indication of the existence at least of tidal interactions, and that the contours of galaxies in A3528 appear to be elongated in the North-South direction, pointing towards the A3530-A3532 pair. From our survey we obtained ~600 new radial velocity determinations: using this sample, we studied the dynamics of the four Abell clusters in this region (A3528, A3530, A3532 and A3535) and derived their mean velocities and velocity dispersions. Moreover we performed a substructure analysis, both bi-dimensional and three-dimensional, of the whole complex. All the characteristics of this structure seem to point toward a merging scenario in an early stage, whose effects on the galaxy population and on the cluster dynamics are not yet evident, contrary to what happens in the nearby A3558 complex, where the merging events are in a rather advanced stage and were already able to induce modifications in the galaxy population.