Radio polarimetry of compact steep spectrum sources at sub-arcsecond resolution^⋆

¹ Istituto di Radioastronomia – INAF, via Gobetti 101, 40129 Bologna, Italy
e-mail: fmantovani@ira.inaf.it
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Los Alamos National Laboratory, Los Alamos, NM 87545, USA
⁴ Cotton College State University, Panbazar, 781 001 Guwahati, India
⁵ National Centre for Radio Astrophysics, TIFR, Post Bag 3, Ganeshkhind, 411 007 Pune, India
⁶ Arecibo Observatory, HC3 Box 53995, 00612 Arecibo, Puerto Rico

Received: 21 November 2012
Accepted: 26 April 2013

Abstract

Aims. We report new Very Large Array (VLA) polarimetric observations of compact steep-spectrum (CSS) sources at 8.4, 15, and 23 GHz.

Methods. Using multi-frequency VLA observations we have derived sub-arcsecond resolution images of the total intensity, polarisation, and rotation measure (RM) distributions.

Results. We present multi-frequency VLA polarisation observations of CSS sources. About half of the sources are point-like even at the resolution of ~0.1 × 0.1 arcsec. The remaining sources have double or triple structure. Low values for the percentage of polarised emission in CSS sources is confirmed. On the average, quasars are more polarised than galaxies. A wide range of RM values have been measured. There are clear indications of very large RMs up to ≈5585 rad m^-2. CSS galaxies are characterized by RM values that are larger than CSS quasars. The majority of the objects show very large values of RM.

Conclusions. The available data on sub-arcsecond-scale rest-frame RM estimates for CSS sources show that these have a wide range of values extending up to ~36 000 rad m^-2. RM estimates indicate an overall density of the magneto-ionic medium larger than classical radio sources.