AGN and starburst radio activity in the A3558 cluster complex

Abstract

We present Very Large Array (VLA) 1.4 GHz (21 cm) observations of the region between the centres of A3558 and A3562, in the major cluster merger complex of the Shapley Concentration. Our final catalogue includes a total of 174 radio sources above the flux density limit of 0.25 mJy b-1. By cross-correlation with optical and spectroscopic catalogues we found 33 optical counterparts belonging to the Shapley Concentration. We investigated the effects of cluster merger on the radio emission properties of the galaxy population by means of the radio source counts and the radio luminosity functions (RLF). We found that the radio source counts are consistent with the field source counts. The RLF of elliptical and S0 galaxies in the region surveyed, is consistent with the "universal" RLF for early-type galaxies. This result suggests that the deficit in radio galaxies found in our previous work over the whole A3558 chain is entirely due to the cluster A3558. A population of faint radio galaxies (log P1.4 GHz(W Hz-1) ≲ 22) is also found. Half of these objects are also blue, suggesting that starburst is the main mechanism driving the radio emission. Finally, we detected 14 spiral radio galaxies, whose ratio between radio and optical emission is similar to those found in galaxies located in rich and dynamically evolved clusters. Our results are briefly discussed in the light of the age and stage of the merger in the A3558 cluster complex.