Turning AGN bubbles into radio relics with sloshing: modeling CR transport with realistic physics

TL;DR

This paper models cosmic-ray transport in galaxy clusters to understand the formation of radio relics, revealing that detailed cosmic ray physics significantly influence the relics' observed shapes.

Contribution

It introduces a more realistic cosmic-ray physics model, including diffusion and Alfvén losses, and assesses its impact on relic morphology in galaxy cluster simulations.

Findings

Including cosmic ray diffusion reduces filamentary relic features.

Pre-existing cosmic-ray distributions influence relic shapes.

Modeling cosmic rays as a separate fluid affects relic morphology.

Abstract

Radio relics are arc-like synchrotron sources at the periphery of galaxy clusters, produced by cosmic-ray electrons in a $\mu$G 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 Alfv\'en 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.