Models of radio galaxies with tangled magnetic fields – I. Calculation of magnetic field transport, Stokes parameters and synchrotron losses.

Abstract

This is the first of two papers describing and discussing numerical simulations of radio sources in which a randomly tangled magnetic field is introduced in the jet, and is then convected passively with the fluid flow. The intrinsic polarization distribution of the source model is therefore determined solely by the distortion of the field by compression and shear in the flow. Such models show up a number of important features which do not appear in models with ordered poloidal, toroidal or helical fields. Our models incorporate synchrotron loss; apart from its intrinsic interest, a small amount of synchrotron loss has the effect of removing the radio emission from small regions where the distortion produces unrealistically high fields. This paper is devoted to calculating the distortion of a frozen-in field by the fluid flow and the synchrotron losses suffered by the relativistic electrons injected with the fluid, and showing how the calculation of the resulting radio emission can be made manageable. The second paper will exhibit and discuss simulations made with various input parameters.