2010A&A...518A..33M

We report new Very Long Baseline Array (VLBA) polarimetric observations of the compact steep-spectrum (CSS) sources 3C119, 3C318, and 3C343 at 5 and 8.4GHz. We analysed our VLBA observations and derived milliarcsecond-resolution images of the total intensity, polarisation, and rotation measure (RM) distributions. The CSS source 3C119, associated with a possible quasar, has source rest-frame RM values up to ∼10200rad/m2 in a region that coincides with a change in the direction of the inner jet. This component is located ∼325pc from the core, which is a variable source with a peaked radio spectrum. For 3C318, which is associated with a galaxy, a rest-frame RM of ∼3030rad/m2 was estimated for the brightest component contributing almost all of the polarised emission. Two more extended components were detected, that contain ``wiggles'' in the jet towards the southern side of the source. The CSS source 3C343 contains two peaks of emission and a curved jet embedded in more diffuse emission. It exhibits complex field directions close to the emission peaks, which are indicative of rest-frame RM values in excess of ≃6000rad/m2. The locations of the cores in 3C318 and 3C343 are unclear. The available data about mas-scale rest-frame RM estimates for CSS sources show that these have a wide range of values extending up to ∼40000rad/m2 in the central region of OQ172, and may be located at projected distances from the core of up to ∼1600pc, as in 3C43 where this feature has a rest-frame RM of ∼14000rad/m2. The RM estimates for the cores of core-dominated radio sources indicate that in addition to responding to an overall density gradient of the magneto-ionic medium, geometry, orientation, and modes of fuelling may also play a significant role. In addition to these effects, the high values of RM in CSS sources are possibly caused by dense clouds of gas interacting with the radio jets. The observed distortions in the radio structures of many CSS sources are consistent with this interpretation.