Simulated Interactions Between Radio Galaxies and Cluster Shocks -- 2: Jet Axes Orthogonal to Shock Normals

TL;DR

This study uses 3D MHD simulations to explore how radio galaxy jets interact with cluster shocks, revealing vortex formation, jet deflection, and implications for radio emission and spectral features.

Contribution

It introduces a detailed simulation framework for orthogonal jet-shock interactions, highlighting vortex dynamics and the effects of ongoing or ceased jet activity.

Findings

Shock disrupts radio galaxy cavities into vortex rings.

Active jets produce bright, aligned radio tails.

Adiabatic compression explains spectral brightening without DSA.

Abstract

We report a 3D MHD simulation study of the interactions between radio galaxies and galaxy-cluster-media shocks in which the incident shock normals are orthogonal to the bipolar AGN jets. Before shock impact, light, supersonic jets inflate lobes (cavities) in a static, uniform ICM. We examine three AGN activity scenarios: 1) continued, steady jet activity; 2) jet source cycled off coincident with shock/radio lobe impact; 3) jet activity ceased well before shock arrival (a "radio phoenix" scenario). The simulations follow relativistic electrons (CRe) introduced by the jets, enabling synthetic radio synchrotron images and spectra. Such encounters can be decomposed into an abrupt shock transition and a subsequent long term post shock wind. Shock impact disrupts the pre-formed, low density RG cavities into two ring vortices embedded in the post shock wind. Dynamical processes cause the vortex pair to merge as they propagate downwind somewhat faster than the wind itself. When the AGN jets remain active ram pressure bends the jets downwind, generating a narrow angle tail morphology aligned with the axis of the vortex ring. The deflected jets do not significantly alter dynamical evolution of the vortex ring. However, active jets and their associated tails do dominate the synchrotron emission, compromising the observability of the vortex structures. Downwind-directed momentum concentrated by the jets impacts and alters the post-encounter shock. In the "radio phoenix" scenario, no DSA of the fossil electron population is required to account for the observed brightening and flattening of the spectra, adiabatic compression effects are sufficient.