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

¹ INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
e-mail: tventuri@ira.inaf.it
² Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133 Milano, Italy
³ INAF – IASF, via Bassini 15, 20133 Milano, Italy
⁴ INAF – Osservatorio Astronomico di Bologna, Via Ranzani 1, 40126 Bologna, Italy
⁵ Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
⁶ Joint Space-Science Institute, University of Maryland, College Park, MD, 20742-2421, USA
⁷ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40126 Bologna, Italy
⁸ National Centre for Radio Astronomy, Tata Institute of Fundamental Research, Post Bag 3, Ganeshkind, 411007 Pune, India

Received: 5 June 2013
Accepted: 3 August 2013

Abstract

Context. We study the interplay between the radio emission associated with the dominant galaxy in clusters and the properties of the surrounding intracluster medium on the basis of its X-ray emission.

Aims. Previous radio observations of the galaxy cluster A 3560, located in the Shapley Concentration core, revealed complex radio emission associated with the brightest cluster member. To understand the origin of this radio emission we performed a detailed multiwavelength study with high-quality proprietary data in the radio and X-ray bands and by means of optical data available in the literature.

Methods. We observed the cluster with the Giant Metrewave Radio Telescope, the Very Large Array, and the Australia Telescope Compact array 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 brightest cluster galaxy (BCG). Furthermore, we observed the cluster with the XMM-Newton and Chandra observatories to derive the properties of the intracluster gas. Finally, we made use of literature data to obtain the bidimensional distribution of the galaxies in the cluster.

Results. The radio emission, associated with the north-eastern nucleus of the dumb-bell BCG, is the result of two components: an active radio galaxy, with jets and lobes, plus aged diffuse emission, which is not refurbished with new electrons 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 distribution shows a spiral-like feature, which we interpret as the signature of gas sloshing. A sub-group is clearly visible in the surface brightness residual map, and this is also supported by the XMM-Newton temperature analysis. The optical bidimensional analysis shows substructure in A 3560. A galaxy clump was detected at the location of the X-ray sub-group, and another group is present south of the cluster core, in the region where the spiral-like feature was detected. 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 A 3560. The aged diffuse emission is strongly affected by the sloshing motion in the intracluster gas and most likely bears information on the trajectory of the cluster BCG during the dynamical evolution of the cluster. 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.