The Origin of Complex Behavior of Linearly Polarized Components in Parsec-scale Jets

Evidence that the magnetic fields of extragalactic jets have a significant fraction of their energy in a random component is briefly summarized, and a detailed model of evolving, jet polarization structures is constructed, based on this picture. The evolving magnetic field structure of an oblique shock complex that forms in a relativistic jet simulation is explored by 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 infer a component following a non-linear trajectory, and with a magnetic field orientation that rotates during evolution. This result highlights the ambiguity in interpreting VLBP data, and illustrates the importance of simulations in providing a framework for proper interpretation of such data. Subject headings: galaxies: jets — hydrodynamics — magnetic fields — polarization — radiative transfer — relativity — shock waves