MODELS OF RADIO GALAXIES WITH TANGLED MAGNETIC-FIELDS .2. NUMERICAL SIMULATIONS AND THEIR INTERPRETATION

This paper describes and discusses numerical simulations of the radio emission from radio galaxies or quasars. In most simulations made hitherto, the emphasis has been on the fluid dynamics of the jet interacting with the ambient circum or intergalactic gas and, where radio images have been shown, they have generally represented the radio emissivity simply as some function of total pressure. In this paper, the fluid dynamics is conventional; the emphasis is on the development of the magnetic field and its consequences for the brightness distribution and polarization of observable radio images. In the models, a randomly tangled magnetic field and an energy spectrum of relativistic electrons are introduced with the jet. The fields and electrons are convected passively with the flow, and synchrotron losses in the electron energy distribution are followed in detail. We find that the magnetic field strength (and therefore also the radio emissivity) varies widely through the source, in ways not directly related to the pressure distribution. The models predict images with high polarization around the periphery of the lobes, and E-vectors normal to the periphery, in agreement with observation, but the polarization over most of the rest of the model source is much higher than is generally observed. Hotspots appear naturally in the model sources, although no diffusive particle acceleration at a 'working surface' is assumed. © Royal Astronomical Society.