MOJAVE – XX. Persistent linear polarization structure in parsec-scale AGN jets

Funding Information: The authors thank the referee John Wardle for constructive comments which helped to improve the manuscript. We thank members of the MOJAVE team for discussions of the paper, Alan Roy for thorough reading of the manuscript and providing useful comments as well as Elena Bazanova for language editing. This study was supported by the Russian Science Foundation grant 21-12-00241. The MOJAVE project was supported by NASA-Fermi grants NNX08AV67G, NNX12A087G, and NNX15AU76G. This work is part of the M2FINDERS project which has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme (grant agreement no 101018682). This research has made use of data from the University of Michigan Radio Astronomy Observatory which has been supported by the University of Michigan and by a series of grants from the National Science Foundation, most recently no. AST-0607523. TS was partly supported by the Academy of Finland projects 274477, 284495, 312496, and 315721. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The Long Baseline Observatory and the National Radio Astronomy Observatory are facilities of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This work made use of the Swinburne University of Technology software correlator (Deller et al. 2011), developed as part of the Australian Major National Research Facilities Programme and operated under licence. Publisher Copyright: © 2023 The Author(s)We analysed the parsec-scale linear polarization properties of 436 active galactic nuclei (AGNs) based on 15 GHz polarimetric Very Long Baseline Array observations. We present polarization and total intensity images averaged over at least five epochs since 1996 January 19 through 2019 August 4. Stacking improves the image sensitivity down to ∼30 μJy beam−1 and effectively fills out the jet cross-section both in total intensity and linear polarization. It delineates the long-term persistent magnetic field configuration and its regularity by restoring spatial distributions of the electric vector position angle (EVPA) and fractional polarization, respectively. On average, about 10 yr of stacking period is needed to reveal the stable and most-complete polarization distribution of a source. We find that the degree of polarization significantly increases down and across the jet towards its edges, typically manifesting U or W-shaped transverse profiles, suggesting a presence of a large-scale helical magnetic field associated with the outflow. In some AGN jets, mainly BL Lacs, we detect quasi-constant fractional polarization profiles across the jet, accompanied by EVPAs that closely follow the outflow. BL Lacs show higher fractional polarization values in their cores and jets than those in quasars up to hectoparsec de-projected scales, while on larger scales, they become comparable. High-synchrotron-peaked BL Lac jets are found to be less polarized than intermediate and low-synchrotron-peaked BL Lacs. The spatial distribution of the EVPAs in BL Lacs tend to align with the local jet direction, while quasars show an excess of orthogonal polarization orientation.Peer reviewe