A 3.5mm Polarimetric Survey of Radio-loud Active Galactic Nuclei
  We present the results from the first large (>100 source) 3.5 mm polarimetric
survey of radio loud active galactic nuclei (AGN). The I, Q, U, and V Stokes
parameter observations were performed with the XPOL polarimeter at the IRAM 30m
Telescope. Our sample consists of 145 flat-radio-spectrum AGN with declination
>-30 deg. (J2000.0) and flux density >~1Jy at 86GHz, as measured at the IRAM 30
m Telescope from 1978 to 1994. We detected linear and circular polarization
(above 3 sigma levels of ~1.6%, and ~0.3%) for 76%, and 6% of the sample,
respectively. We find a clear excess in degree of linear polarization detected
at 86 GHz with regard to that at 15 GHz by a factor of ~2. Over our entire
source sample, the luminosity of the jets is inversely proportional to the
degree of linear polarization. Consistent with previous findings claiming
larger Doppler factors for brighter gamma-ray blazars, quasars listed in our
sample, and in the Fermi-LBAS catalog, show larger luminosities than non-LBAS
ones, but our data do not allow us to confirm the same for BL Lac objects. We
do not find a clear relation between the linear polarization angle and the jet
structural position angle for any source class in our sample. We interpret this
as the consequence of a markedly non-axisymmetric character of the 3 mm
emitting region in the jets. We find that intrinsic circular polarization is
the most likely mechanism for generation of the circular polarization detected
in our observations. Our new data can be used to estimate the 3 mm AGN
contribution to measurements of the linear polarization of the cosmic microwave
background, such as those performed by the Planck satellite.
