Cosmic-Ray Acceleration and Magnetic Fields in Galaxy Clusters and Beyond: Insights from Radio Observations

Abstract

The discovery of diffuse radio emission in galaxy clusters proved the existence of energetic cosmic-ray electrons and cosmic magnetic fields on Mpc-scales in the Universe. Furthermore, both magnetic fields and cosmic-ray electrons are predicted to exist beyond galaxy clusters, namely, in the filaments and voids of the cosmic web. Recent detection of diffuse radio emission in intercluster bridges—the region between two merging clusters—strengthens the theory that both cosmic magnetic fields and cosmic-ray electrons exist on these large scales. Radio observations are our most powerful tool to study cosmic magnetic fields and cosmic-ray electrons in the Universe. The recent improvements in radio astronomy, including the exploration of the low-frequency radio sky, have led to the discovery of countless new radio sources, and hence a new understanding of the origin and evolution of cosmic magnetic fields and cosmic-ray electrons. In this contribution, we summarise the newest discoveries in the field. Furthermore, we discuss what these new radio observations teach us about cosmic magnetic fields and cosmic rays in galaxy clusters and beyond.

Search for GeV gamma-ray emission from SPT-SZ selected galaxy clusters with 15 years of Fermi-LAT data

“…They are also giant reservoirs of high energy relativistic cosmic rays (CRs), i.e. relativistic electrons and protons swarming in the hot ionized Intra-Cluster Medium (ICM) [12,13]. Evidence for the acceleration of cosmic ray electrons comes from the observations of radio relics within clusters [13,14].…”

“…relativistic electrons and protons swarming in the hot ionized Intra-Cluster Medium (ICM) [12,13]. Evidence for the acceleration of cosmic ray electrons comes from the observations of radio relics within clusters [13,14]. These relics result from the shock waves generated during cluster mergers, accelerating particles to extreme energies.…”