Galaxy clusters enveloped by vast volumes of relativistic electrons

TL;DR

This paper reports the discovery of extensive diffuse radio emission in galaxy clusters, indicating that relativistic electrons and magnetic fields extend far beyond the known radio halos, revealing new insights into cluster environments.

Contribution

It presents observations of galaxy clusters with larger, more diffuse radio emissions, expanding understanding of relativistic electrons and magnetic fields beyond traditional radio halos.

Findings

Relativistic electrons and magnetic fields extend 30 times beyond radio halos.

Diffuse emission has about 20 times lower emissivity than radio halos.

Outer cluster regions have different physical conditions from the inner halos.

Abstract

The central regions of galaxy clusters are permeated by magnetic fields and filled with relativistic electrons. When clusters merge, the magnetic fields are amplified and relativistic electrons are re-accelerated by turbulence in the intra cluster medium. These electrons reach energies of 1 -- 10 GeV and, in the presence of magnetic fields, produce diffuse radio halos that typically cover an area of ~1 square Mpc. Here we report observations of four clusters whose radio halos are embedded in much more extended, diffuse radio emission, filling a volume 30 times larger than that of radio halos. The emissivity in these larger features is about 20 times lower than the emissivity in radio halos. We conclude that relativistic electrons and magnetic fields extend far beyond radio halos, and that the physical conditions in the outer regions of the clusters are quite different from those in the radio halos.