The origin of complex behavior of linearly polarized components in parsec-scale jets

I briefly summarize the evidence that the magnetic fields of extragalactic jets have a significant fraction of their energy in a random component and construct a detailed model of evolving jet polarization structures based on this picture. The evolving magnetic field structure of an oblique shock complex that forms in a relativistic jet simulation is explored using velocity data from the hydrodynamical simulation to advect an initially random magnetic field distribution. Radiative transfer calculations reveal that emission from a propagating region of magnetic field, " ordered'' by the shock and lying approximately transverse to the flow direction, merges with that from an evolving sheared region at the flow periphery. If such a flow were barely resolved, observation would suggest evolution from a somewhat oblique to a more longitudinal magnetic field structure with respect to the flow axis, while higher resolution observations would reveal a component following a nonlinear trajectory and with a magnetic field orientation that rotates during evolution. This result highlights the ambiguity in interpreting very long baseline polarimetry ( VLBP) data and illustrates the importance of simulations in providing a framework for proper interpretation of such data.