The interpretation of asymmetric depolarization in extragalactic radio sources

We discuss various interpretations of the effect found in powerful double radio sources with one-sided jets whereby the depolarization is systematically stronger on the counter-jet side. Depolarization by gas located within the source is unlikely to be the cause of the asymmetry. Line-emitting gas, though often associated with depolarization in radio galaxies, is not systematically stronger on the counter-jet side. We interpret the asymmetry in terms of a halo of hot gas surrounding the radio source. If the visible jet is on the near side of the source, as required for the relativistic beaming hypothesis, it will be seen through less depolarizing gas. We have investigated halo models, using density information from X-ray data and assuming the magnetic-field energy to scale as the gas density. Tangling of the magnetic field due to turbulence is shown to be important chiefly on scales of a few kpc. (author)