ATCA observations of the MACS-Planck Radio Halo Cluster Project

I. New detection of a radio halo in PLCK G285.0-23.7 ^⋆

¹ Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Bvd de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
e-mail: Gerardo.Martinez-Aviles@oca.eu
² School of Chemical & Physical Sciences, Victoria University of Wellington, PO Box 600, 6140 Wellington, New Zealand
³ INAF−Osservatorio di Radioastronomia, via P. Gobetti 101, 40129 Bologna, Italy
⁴ Department of Physics and Astronomy, UniBO, via Ranzani 1, 40127 Bologna, Italy
⁵ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 Leiden, The Netherlands
⁶ Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
⁷ Institut d’Astrophysique Spatiale, CNRS, Univ. Paris-Sud, Université Paris-Saclay, Bât. 121, 91405 Orsay Cedex, France

Received: 25 April 2016
Accepted: 17 June 2016

Abstract

Aims. We investigate the possible presence of diffuse radio emission in the intermediate redshift, massive cluster PLCK G285.0-23.7 (z = 0.39, M₅₀₀ = 8.39 × 10¹⁴M_⊙).

Methods. Our 16 cm-band ATCA observations of PLCK G285.0-23.7 allow us to reach a rms noise level of ~11 μJy/beam on the wide-band (1.1–3.1 GHz), full-resolution (~5 arcsec) image of the cluster, making it one of the deepest ATCA images yet published. We also re-image visibilities at lower resolution in order to achieve a better sensitivity to low-surface-brightness extended radio sources.

Results. We detect one of the lowest luminosity radio halos known at z > 0.35, characterised by a slight offset from the well-studied 1.4 GHz radio power vs. cluster mass correlation. Similarly to most known radio-loud clusters (i.e. those hosting diffuse non-thermal sources), PLCK G285.0-23.7 has a disturbed dynamical state. Our analysis reveals a similarly elongated X-ray and radio morphology. While the size of the radio halo in PLCK G285.0-23.7 is smaller than lower redshift radio-loud clusters in the same mass range, it shows a similar correlation with the cluster virial radius, as expected in the framework of hierarchical structure formation.