Discovery of large-scale diffuse radio emission and of a new galaxy cluster in the surroundings of MACS J0520.7-1328

¹ Laboratoire Lagrange, UMR 7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur, 06300 Nice, France
e-mail: giulia.macario@oca.eu
² Jansky Fellow of the National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA
³ National Radio Astronomy Observatory, PO Box O, 1003 Lopezville Road, Socorro, NM 87801-0387, USA
⁴ Dipartimento di Fisica, Università degli Studi di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
⁵ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁶ Joint Space-Science Institute, University of Maryland, College Park, MD 20742-2421, USA
⁷ INAF-Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
⁸ Dipartimento di Fisica e Astronomia, via Ranzani 1, 40127 Bologna, Italy
⁹ School of Chemical & Physical Sciences, Victoria University of Wellington, PO Box 600, 6140 Wellington, New Zealand
¹⁰ Laboratoire AIM, IRFU/Service d’Astrophysique CEA/DSM CNRS Université Paris Diderot, Bt. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
¹¹ Department of Physics and Astronomy, University of Iowa, 203 Van Allen Hall, Iowa City, IA 52242, USA

Received: 17 December 2013
Accepted: 17 February 2014

Abstract

We report the discovery of large-scale diffuse radio emission south-east of the galaxy cluster MACS J0520.7-1328, detected through high-sensitivity Giant Metrewave Radio Telescope 323 MHz observations. This emission is dominated by an elongated diffuse radio source and surrounded by other features of lower surface brightness. Patches of these faint sources are marginally detected in a 1.4 GHz image obtained through a re-analysis of archival NVSS data. Interestingly, the elongated radio source coincides with a previously unclassified extended X-ray source. We perform a multi-wavelength analysis based on archival infrared, optical, and X-ray Chandra data. We find that this source is a low-temperature (~3.6 keV) cluster of galaxies, with indications of a disturbed dynamical state, located at a redshift that is consistent with the one of the main galaxy cluster MACS J0520.7-132 (z = 0.336). We suggest that the diffuse radio emission is associated to non-thermal components in the intracluster and intergalactic medium in and around the newly detected cluster. We are planning deeper multi-wavelength and multi-frequency radio observations to accurately investigate the dynamical scenario of the two clusters and to address the nature of the complex radio emission more precisely.