Shocked Narrow-Angle Tail Radio Galaxies: Simulations and Emissions

Abstract

We present a numerical study of the interactions between the elongated AGN outflows representing an evolved, narrow-angle tail (NAT) radio galaxy and planar, transverse ICM shock fronts characteristic of those induced by galaxy cluster mergers (incident Mach numbers 2 - 4). The simulated NAT formation was reported previously in \cite{on19a}. Our simulations utilize a three-dimensional, Eulerian magnetohydrodynamic code along with energy-dependent Eulerian transport of passive cosmic ray electrons. Our analysis of the shock/NAT interaction applies a Riemann problem-based theoretical model to interpret complex shock front behavior during passage through the highly heterogeneous structures of the simulated NAT tails. In addition to shock compression, shock-induced vortical motions are observed within the tails that contribute to coherent turbulent dynamo processes that continue to amplify the magnetic fields in the tails well after initial shock compression. We analyze synthetic radio observations spanning the NAT-shock interaction period, and examine the brightness, spectral and polarization properties of our shock-rejuvenated radio tails, as well as the extent to which the pre-shock states of the plasma and particle populations in our tails influence post-shock observations. Finally, we evaluate our findings in the possible context of a physical analogy to our simulated NAT providing the precursor to a cluster ``radio relic'' associated with an impacting ICM shock.