Broadband radio spectro-polarimetric observations of high Faraday
  rotation measure AGN
  We present broadband polarimetric observations of a sample of high Faraday
rotation measure (RM) AGN using the VLA telescope from 1 to 2 GHz, and 4 to 12
GHz. The sample (14 sources) consists of compact sources (linear resolution
smaller than ~ 5 kpc) that are unpolarized at 1.4 GHz in the NVSS. Total
intensity data have been modelled using combination of synchrotron components,
revealing complex structure in their radio spectra. Depolarization modelling,
through the so called qu-fitting, have been performed on the polarized data
using an equation that attempts to simplify the process of fitting many
different depolarization models that we can divide into two major categories:
External Depolarization and Internal Depolarization models. Understanding which
of the two mechanisms are the most representative, would help the qualitative
understanding of the AGN jet environment, whether it is embedded in a dense
external magnetoionic medium or if it is the jet-wind that causes the high RM
and strong depolarization. This could help to probe the jet magnetic field
geometry (e.g. helical or otherwise). This new high-sensitivity data, shows a
complicated behaviour in the total intensity and polarization radio spectrum of
individual sources. We observed the presence of several synchrotron components
and Faraday components in their total intensity and polarized spectra. For the
majority of our targets, (12 sources) the depolarization seems to be caused by
a turbulent magnetic field. Thus, our main selection criteria (lack of
polarization at 1.4 GHz in the NVSS), results in a sample of sources with very
large RMs and depolarization due to turbulent magnetic fields local to the
source. We show how the new qu-fitting technique can be used to probe the
magnetised radio source environment and to spectrally resolve the polarized
components of unresolved radio sources.
