2007/11/28 by D. C. Gabuzda, V. M. Vitrishchak, M. Mahmud +2 · 1 citation
Physics and Astronomy · #Active galactic nucleus #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Circular polarization #Faraday effect #Galaxies: Formation, Evolution, Phenomena #Galaxy #Helicity #Laser #Linear polarization #Magnetic field #Optics #Physics #Pitch angle #Polarization (electrochemistry) #Radio Astronomy Observations and Technology #Viewing angle #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2007.12773.x
24 pages, 6 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS)
arxiv created 2007/11/28 · openalex publication_date 2008/03/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
Homan & Lister have recently published circular polarization (CP) detections for 34 objects in the MOJAVE sample – a set of bright, compact active galactic nuclei (AGN) being monitored by the Very Long Baseline Array at 15 GHz. We report the detection of 15-GHz parsec-scale CP in two more AGN (3C 345 and 2231+114), and confirm the MOJAVE detection of CP in 1633+382. It is generally believed that the most likely mechanism for the generation of this CP is Faraday conversion of linear polarization (LP) to CP. A helical jet magnetic field (B field) geometry can facilitate this process – linearly polarized emission from the far side of the jet is converted to CP as it passes through the magnetized plasma at the front side of the jet on its way towards the observer. In this case, the sign of the generated CP is essentially determined by the pitch angle and helicity of the helical B field. We have determined the pitch-angle regimes and helicities of the helical jet B fields in eight AGN for which parsec-scale CP has been detected, and used them to predict the expected CP signs for these AGN if the CP is generated via conversion in these helical fields. We have obtained the intriguing result that our predictions agree with the observed signs in all eight cases, provided that the longitudinal B field components in the jets correspond to south magnetic poles. This clearly non-random pattern demonstrates that the observed CP in AGN is directly associated with the presence of helical jet B fields. These results suggest that helical B fields are ubiquitous in AGN jets.