Letter to the Editor

Detection of diffuse radio emission at large distance from the center of the galaxy cluster A 2255

¹ Kapteyn Institute, Postbus 800, 9700 AV Groningen, The Netherlands e-mail: pizzo@astro.rug.nl
² ASTRON, Postbus 2, 7990 AA Dwingeloo, The Netherlands
³ Istituto di radioastronomia-CNR/INAF, via Gobetti 101, 40129 Bologna, Italy
⁴ INAF-Osservatorio astronomico di Cagliari, Poggio dei Pini, Strada 54, 09012 Capoterra (CA), Italy

Received: 21 December 2007
Accepted: 21 February 2008

Abstract

Aims. Low-frequency radio observations of galaxy clusters are the key to detecting the diffuse extended emission associated with them. The presence and properties of such radio sources in galaxy clusters reveal the existence of magnetic fields on a large scale and allow theories to be tested concerning both the origin of relativistic particles in the ICM and their propagation.

Methods. A deep radio observation of the A 2255 galaxy cluster was carried out at 85 cm with the WSRT. The good UV-coverage and sensitivity achieved by these observations allowed us to image the complex structure of the low-brightness, extended cluster sources (radio halo and relic).

Results. These sources show a larger extent than what has been imaged so far at this frequency, with two new structures located SW and NW of the cluster center and at projected distances of 2 Mpc from it.

Conclusions. The physical properties of the newly detected structures, together with the active dynamical state of the cluster, support a connection with large-scale structure (LSS) formation shocks.