Detection of diffuse radio emission in the galaxy clusters A800, A910, A1550, and CL 1446+26

¹ INAF – Osservatorio Astronomico di Cagliari, Strada 54, Loc. Poggio dei Pini, 09012 Capoterra ( Ca), Italy
e-mail: fgovoni@ira.inaf.it
² Laboratoire Lagrange, UMR7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur, 06300 Nice, France
³ INAF – Istituto di Radioastronomia, via P. Gobetti 101, 40129 Bologna, Italy
⁴ Dipartimento di Fisica, Università degli Studi di Cagliari, Cittadella Universitaria, 09042 Monserrato ( CA), Italy
⁵ Dipartimento di Astronomia, Università degli Studi di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁶ National Radio Astronomy Observatory, Socorro, NM 87801, USA

Received: 2 March 2012
Accepted: 10 July 2012

Abstract

Context. Radio halos are elusive sources located at the center of merging galaxy clusters. To date, only about 40 radio halos are known, thus the discovery of new halos provides important insights into this class of sources.

Aims. To improve the quality of the statistics of radio halos, we investigate the radio continuum emission of a sample of galaxy clusters.

Methods. We analyzed archival Very Large Array observations at 1.4 GHz, with a resolution of ≃ 1′. These observations were complemented by X-ray, optical, and higher-resolution radio data, leading to the detection of a new radio halo in the central region of A800 and A1550. We discovered a radio relic in the periphery of A910, and finally revealed both a halo and a relic in CL1446+26.

Results. The clusters hosting these new halos show an offset between the radio and the X-ray peak. By analyzing this offset statistically, we find that radio halos can be quite asymmetric with respect to the X-ray gas distribution, with an average radio-X-ray displacement of about 180 kpc. When the offsets are normalized by the halo size, there is a tendency for smaller halos to have larger displacements.