Radio emission at the centre of the galaxy cluster Abell 3560: evidence for core sloshing?

Abstract

Previous radio observations of the galaxy cluster A3560 in the Shapley Concentration showed complex radio emission associated with the brightest cluster member.To understand its origin we observed it with the GMRT, the VLA and ATCA at 240 and 610 MHz, 1.28,1.4, 2.3,4.8 and 8.4 GHz, and performed a detailed morphological and spectral study of the radio emission associated with the BCG. We also observed the cluster with XMM-Newton and Chandra to derive the properties of the ICM. The radio emission of the N-E nucleus of the dumb-bell BCG shows an active radio galaxy, plus aged diffuse emission, which is not refurbished at present. Our Chandra data show that the radio active nucleus of the BCG has extended X-ray emission, which we classify as a low-luminosity corona. A residual image of the XMM-Newton brightness shows the presence of a spiral-like feature, which we interpret as the signature of gas sloshing. The presence of a subgroup is clear in the surface brightness residual map, and in the XMM-Newton temperature analysis. The optical 2D analysis shows substructure in A3560. A galaxy clump was found at the location of the X-ray subgroup, and another group is present south of the cluster core, close to the spiral-like feature. The aged part of the radio emission closely follows the spiral pattern of the X-ray residual brightness distribution, while the two active radio lobes are bent in a completely different direction. We conclude that the complex radio emission associated with the cluster BCG is the result of a minor merger event in A3560. The aged diffuse emission is strongly affected by the sloshing motion in the ICM. On the other hand, the bent jets and lobes of the current radio AGN activity may reflect a complex gas velocity field in the innermost cluster regions and/or sloshing-induced oscillations in the motion of the cD galaxy.Comment: 15 pages, 8 figures, 5 tables, A&A in pres