Turning AGN Bubbles into Radio Relics with Sloshing: Modeling CR Transport with Realistic Physics

Abstract

Radio relics are arc-like synchrotron sources at the periphery of galaxy clusters, produced by cosmic-ray electrons in a μG magnetic field, which are believed to have been (re-)accelerated by merger shock fronts. However, not all relics appear at the same location as shocks as seen in the X-ray. In a previous work, we suggested that the shape of some relics may result from the pre-existing spatial distribution of cosmic-ray electrons, and tested this hypothesis using simulations by launching AGN jets into a cluster atmosphere with sloshing gas motions generated by a previous merger event. We showed that these motions could transport the cosmic ray-enriched material of the AGN bubbles to large radii and stretch it in a tangential direction, producing a filamentary shape resembling a radio relic. In this work, we improve our physical description for the cosmic rays by modeling them as a separate fluid which undergoes diffusion and Alfvén losses. We find that, including this additional cosmic ray physics significantly diminishes the appearance of these filamentary features, showing that our original hypothesis is sensitive to the modeling of cosmic ray physics in the intracluster medium.

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

“…To overcome this efficiency problem, it has been proposed that, in general, relics are produced by the re-acceleration of a pre-existing population of fossil cosmic-ray electrons. Such a population of fossil cosmic rays could have been produced by several processes, including the injection of cosmic rays by radio galaxies, the shock acceleration by previous merger events, and the energisation by sloshing motions [177,[190][191][192][193][194].…”

Discovery of A Large-scale Bent Radio Jet in the Merging Cluster A514

“…We use this bubble gas to describe the redistribution of fossil CRe injected by a cluster AGN. This passive tracer is a simple model, which does not include a physical model that can modify the substructures of the bubble or the ICM itself (e.g., ZuHone et al 2021a). However, we assume the spatial extent of the redistributed bubble can roughly describe the extent of the redistributed nonthermal plasma as the nonthermal plasma is known to follow the ICM gas flows after it has become mixed with the thermal plasma (e.g., Botteon et al 2023).…”

New Window on the Radio Emission from Galaxies, Clusters and Cosmic Web—Conference Summary

“…By improving the physical description for the cosmic rays, the filamentary features diminish. Therefore, the modeling of cosmic ray physics in the intracluster medium strongly affects the appearance of a radio relic [8].…”