Radial velocities in A2744

We find evidence that this cluster is far from dynamical equilibrium, as shown by the non Gaussianity of the velocity distribution, the presence of a velocity gradient and a significant substructure. Our analysis shows the presence of two galaxy-clumps of different mean LOS velocities DeltaV~4000km/s. We detect a main, low-velocity clump with sigma_V_~1200-1300km/s and a secondary, high-velocity clump with sigma_V_=500-800km/s and located in the S-SW cluster region.

We estimate a cluster mass within 1Mpc of 1.4-2.4M_{sun}_, depending on the model adopted to describe the cluster dynamics. Our results suggest a merging scenario of two clumps with a mass ratio of 3:1 and a LOS impact velocity of DeltaV_rf_~3000km/s, likely observed just after the core passage. The merging is occuring roughly in the NS direction with the axis close to the LOS.

This scenario agrees with that proposed on the basis of recent Chandra results in its general lines although pointing out for a somewhat more advanced merging phase. Our conclusions support the view of the connection between extended radio emission and energetic merging phenomena in galaxy clusters.