A numerical study of the impact of jet magnetic topology on radio galaxy evolution

Abstract

ABSTRACT The propagation of active galactic nucleus jets depends both on the environment into which they propagate and on their internal structure. To test the impact that different magnetic topologies have on the observable properties of radio galaxies on kpc scales, we conducted a series of magnetohydrodynamic simulations of jets injected with different magnetic field configurations propagating into a gaseous atmosphere modelled on the Perseus cluster. The simulations show that the structure of the field affects the collimation and propagation of the jets on cluster scales and thus the morphology of the radio lobes inflated by the jets, due to both magnetic collimation and the development of dynamical instabilities in jets with different magnetic topologies. In all cases, the simulations show a distinct reversal of the synchrotron spectral age gradient in the radio lobes about a dynamical time after the jets turn off due to large-scale circulation inside the radio lobe, driven primarily by buoyancy, which could provide a way to constrain the age of radio sources in cluster environments without the need for detailed spectral modelling and thus constrain the radio-mode feedback efficiency. We suggest a robust diagnostic to search for such age gradients in multifrequency radio data.