2003MNRAS.339..360H

I present high-frequency polarimetric radio observations of the radio galaxy 3C 171, in which depolarization is associated with an extended emission-line region. The radio hotspots, known to be depolarized at low radio frequencies, become significantly polarized above (observer's frame) frequencies of 15 GHz. There is some evidence that some of the Faraday rotation structure associated with the emission-line regions is being resolved at the highest resolutions (0.1 arcsec, or 400 pc); however, the majority remains unresolved. Using the new radio data and a simple model for the nature of the depolarizing screen, it is possible to place some constraints on the nature of the medium responsible for the depolarization. I argue that it is most likely that the depolarization is due not to the emission-line material itself but to a second, less dense, hot phase of the shocked interstellar medium, and derive some limits on its density and temperature.