Parsec-scale jet polarization properties of a complete sample of active galactic nuclei at 43 GHz.
Abstract (from CDS):
We present results from the highest resolution polarization imaging survey of a complete sample of extragalactic radio sources carried out to date. Our sample consists of a statistically complete flat-spectrum subset of 32 active galactic nuclei (AGNs) from the Pearson-Readhead survey, which has been studied at a variety of wavelengths and resolutions, including space-VLBI. Our observations were made with the VLBA at 43 GHz, at which the relatively higher resolution and weaker opacity effects have allowed us to probe magnetic field structures in the jets of these AGNs much closer to the central engine than in previous studies. At 43 GHz, the bulk of the total intensity and polarized emission in most flat-spectrum AGNs originates from an unresolved core component located at the extreme end of a faint jet. The luminosity of the core is positively correlated with the total source luminosity in soft X-rays, in the optical, and at 5 GHz. The most strongly polarized cores display electric vectors that are preferentially aligned with the jet axis, which is consistent with a strong transverse shock that enhances the perpendicular component of the jet magnetic field. Sources with highly polarized cores also tend to have high optical polarizations and flatter overall radio spectra. Approximately half of the AGNs in our sample display apparently bent jet morphologies that are suggestive of streaming motions along a helical path. The straightest jets in the sample tend to display slower superluminal speeds than those that are significantly bent. Our observations also show that intrinsic differences in the jet magnetic field properties of BL Lac objects and quasars previously seen on scales of tens of milliarcseconds are also present in regions much closer to the base of the jet.
Galaxies: BL Lacertae Objects: General - Galaxies: Active - Galaxies: Jets - Polarization - Galaxies: Quasars: General - Radio Continuum: Galaxies