Unravelling the physics of particle acceleration and feedback in galaxy clusters and the cosmic web

ended

We will unravel the origin of cosmic magnetic fields, the physics of particle acceleration in dilute plasmas, and the nature of AGN feedback with state-of-the-art radio telescopes. With the enormous gains in sensitivity, survey speed, and resolution of these telescopes – combined with recent breakthroughs that correct for phased-arrays and the Earth’s distorting ionosphere – we can now take the next big step in this field. Cosmic web filaments and galaxy clusters are the Universe’s largest structures. Clusters grow by a sequence of mergers, generating shock waves and turbulence which heat the cluster plasma. In merging clusters, cosmic rays are accelerated to extreme energies, producing Mpc-size diffuse synchrotron emitting sources. However, these acceleration processes are still poorly understood. Clusters are also heated by AGN feedback from radio galaxies, but the total energy input by feedback and its evolution over cosmic time are unknown. We will construct the largest low-frequency sample of galaxy clusters to (1) establish how particles are accelerated in cluster plasmas, (2) quantify how the cosmic ray content scales with cluster mass, (3) determine the importance of AGN fossil plasma in the acceleration processes, (4) characterize current and past episodes of AGN feedback, and (5) determine the evolution of feedback up to the epoch of cluster formation (z=1-2). These results will be essential to understand cluster formation and its associated energy budget. As in clusters, cosmic web accretion shocks should also accelerate particles producing radio emission. Based on the deepest low-frequency images ever produced, we will (5) carry out the first studies of these giant accelerators, opening up a new window on the elusive warm-hot intergalactic medium, where many of the cosmic baryons reside. Even more important, (6) we aim to obtain measurements of the intergalactic magnetic field, providing key constraints on the origin of our Universe’s magnetic fields.