Discovery of intergalactic radio emission in the Coma–A1367 supercluster

Abstract

THE Coma cluster is a rich cluster of galaxies nested in an even larger supercluster of galaxies. The plane of the supercluster seems to be defined by the Coma cluster itself and another galaxy cluster, Abell 1367, which lies ∼40 Mpc farther west1, 2. The largest structures known are the giant voids and superclusters which are as large as 70h−175 Mpc (refs 3–5). The Coma cluster of galaxies seems to be located on the rim of a giant void6 in the three-dimensional distribution of galaxies. Here we describe the detection of faint, supercluster-scale radio emission at 326 MHz that extends between the Coma cluster of galaxies (Abell 1656) and the Abell 1367 cluster and which is apparently not associated with any individual galaxy system in the complex. The radiation's synchrotron origin implies the existence of a large-scale intercluster magnetic field with an estimated strength of 0.3–0.6 μG, which is remarkably strong. The synchrotron-emitting relativistic electrons cannot be older than a few times 108 yr, but we speculate that the magnetic field is the fossil of a pre-galactic primaeval field, which was amplified in the course of the formation of intergalactic voids and superclusters.