Radio polarimetry of 3C 119, 3C 318, and 3C 343 at milliarcsecond resolution

¹ Istituto di Radioastronomia – INAF, via Gobetti 101, 40129 Bologna, Italy e-mail: fmantovani@ira.inaf.it
² Los Alamos National Laboratory, Los Alamos, NM 87545, USA
³ National Centre for Radio Astrophysics, TIFR, Post Bag 3, Ganeshkhind, Pune 411 007, India
⁴ ICRAR, University of Western Australia, Crawley, WA 6009, Australia
⁵ Arecibo Observatory, HC3 Box 53995, Arecibo, Puerto Rico 00612

Received: 10 March 2010
Accepted: 4 May 2010

Abstract

Aims. We report new Very Long Baseline Array (VLBA) polarimetric observations of the compact steep-spectrum (CSS) sources 3C 119, 3C 318, and 3C 343 at 5 and 8.4 GHz.

Methods. We analysed our VLBA observations and derived milliarcsecond-resolution images of the total intensity, polarisation, and rotation measure (RM) distributions.

Results. The CSS source 3C 119, associated with a possible quasar, has source rest-frame RM values up to ~10 200 rad m^-2 in a region that coincides with a change in the direction of the inner jet. This component is located ~325 pc from the core, which is a variable source with a peaked radio spectrum. For 3C 318, which is associated with a galaxy, a rest-frame RM of ~3030 rad m^-2 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 3C 343 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 ≈6000 rad m^-2. The locations of the cores in 3C 318 and 3C 343 are unclear.

Conclusions. 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 ~40 000 rad m^-2 in the central region of OQ172, and may be located at projected distances from the core of up to ~1600 pc, as in 3C 43 where this feature has a rest-frame RM of ~14 000 rad m^-2. 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.