Common origin for radio relics and halos: galaxy cluster-wide, homogeneous cosmic-ray distribution, and evolving magnetic fields

Understand

Some galaxy clusters show diffuse radio emission in the form of peripheral relics (so far attributed to primary, shock-(re)accelerated electrons) or central halos.

• Analysing radio and X-ray data from the literature, we find new connections between halos and relics, such as a universal linear relation between their peak radio brightness and the gas column density.
• Our results indicate that halos, relics, and halo-relic bridges in a cluster, all arise from the same, homogeneous cosmic ray (CR) ion (CRI) distribution.
• We analytically derive the signature of synchrotron emission from secondary electrons and positrons (CREs) produced in hadronic CRI collisions, for an arbitrary magnetic field evolution.