Revealing the magnetic field in a distant galaxy cluster: discovery of the complex radio emission from MACS J0717.5 +3745

TL;DR

This study reveals the complex radio emission and magnetic field structure in the distant galaxy cluster MACS J0717.5+3745, highlighting its powerful radio halo and polarized emission, using multi-frequency radio and X-ray observations.

Contribution

First detailed multi-frequency analysis of radio and X-ray data unveiling the complex non-thermal phenomena in a distant, merging galaxy cluster.

Findings

Detection of the most distant and powerful radio halo.

First polarization detection in this cluster's radio emission.

Identification of large-scale ordered magnetic fields.

Abstract

Aims. To study at multiple frequencies the radio emission arising from the massive galaxy cluster MACS J0717.5+3745 (z=0.55). Known to be an extremely complex cluster merger, the system is uniquely suited for an investigation of the phenomena at work in the intra-cluster medium (ICM) during cluster collisions. Methods. We use multi-frequency and multi-resolution data obtained with the Very Large Array radio telescope, and X-ray features revealed by Chandra, to probe the non-thermal and thermal components of the ICM, their relations and interactions. Results. The cluster shows highly complex radio emission. A bright, giant radio halo is detected at frequencies as high as 4.8 GHz. MACS J0717.5+3745 is the most distant cluster currently known to host a radio halo. This radio halo is also the most powerful ever observed, and the second case for which polarized radio emission has been detected, indicating that the magnetic field is ordered on large scales.