Diffuse radio emission in MACS J0025.4–1222: the effect of a major merger on bulk separation of ICM components

¹ Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
² CSIRO Astronomy & Space Science, 26 Dick Perry Avenue, Kensington, WA 6151, Australia
e-mail: chris.riseley@csiro.au
³ School of Physics & Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
⁴ Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁵ Astronomical Institute Anton Pannekoek, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands

Received: 15 August 2016
Accepted: 2 November 2016

Abstract

Context. Mergers of galaxy clusters are among the most energetic events in the Universe. These events have significant impact on the intra-cluster medium, depositing vast amounts of energy, often in the form of shocks, as well as heavily influencing the properties of the constituent galaxy population. Many clusters have been shown to host large-scale diffuse radio emission, known variously as radio haloes and relics. These sources arise as a result of electron (re-)acceleration in cluster-scale magnetic fields, although the processes by which this occurs are still poorly understood.

Aims. We present new, deep radio observations of the high-redshift galaxy cluster MACS J0025.4−1222, taken with the Giant Metrewave Radio Telescope (GMRT) at 325 MHz, as well as a new analysis of all archival Chandra X-ray observations. We aim to investigate the potential of diffuse radio emission and categorise the radio population of this cluster, which has only been covered previously by shallow radio surveys.

Methods. We produced low-resolution maps of MACS J0025.4−1222 through a combination of uv-tapering and subtracting the compact source population. Radial surface brightness and mass profiles were derived from the Chandra data. We also derived a 2D map of the intracluster medium temperature.

Results. For the first time, two sources of diffuse radio emission are detected in MACS J0025.4−1222, on linear scales of several hundred kpc. Given the redshift of the cluster and the assumed cosmology, these sources appear to be consistent with established trends in power scaling relations for radio relics. The X-ray temperature map presents evidence of an asymmetric temperature profile and tentative identification of a temperature jump associated with one relic.

Conclusions. We classify the pair of diffuse radio sources in this cluster as a pair of radio relics, given their consistency with scaling relations, location toward the cluster outskirts, and the available X-ray data.