A 3.5mm Polarimetric Survey of Radio Loud AGN
Abstract
We present the results from the first large 3.5mm 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, containing 146 sources, essentially consists of all known flat-radio-spectrum AGN with declination >-30 deg. (J2000.0) and flux density >~1Jy at ~86GHz, as measured at the IRAM 30m 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 show a clear excess of the linear polarization degree detected at 86GHz with regard to that at 15GHz by a factor of ~2. Quasars and LBAS (LAT Bright AGN Sample) blazars in our sample show larger luminosity of their jets for lower linear polarization degree. Consistent with previous findings claiming larger Doppler factors for brighter gamma-ray blazars, LBAS blazars in our sample show larger luminosity than non detected ones in our sample, but we show that they are only quasars, and not BL Lac objects, which contribute to distribute LBAS blazars towards larger luminosities. We do not find a clear relation between the linear polarization angle and the jet structural position angle of any source class in our sample, that we interpret as a markedly non axisymmetric character of the 3mm emiting region in their 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 are relevant, and can be used, to estimate the 3.5mm AGN contribution to linear polarization CMB measurements as those performed by the Planck satellite.Keywords
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