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Galaxies 2018, 6(1), 9; https://doi.org/10.3390/galaxies6010009

Determining the Jet Poloidal B Field and Black-Hole Rotation Directions in AGNs

Physics Department, University College Cork, Cork, Ireland
Received: 21 October 2017 / Revised: 16 December 2017 / Accepted: 9 January 2018 / Published: 12 January 2018
(This article belongs to the Special Issue Polarised Emission from Astrophysical Jets)
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Abstract

It is theoretically expected that active galactic nucleus (AGN) jets should carry helical magnetic (B) fields, which arise due to the rotation of the central black hole and accretion disk combined with the jet outflow. The direction of the toroidal component of the helical B field B φ is determined by the direction of the poloidal component B p of the initial seed field that is “wound up” and the direction of rotation of the central black hole and accretion disk. The presence of the jet’s helical B field can be manifest both through the presence of Faraday rotation gradients across the jet, and the presence of appreciable circular polarization, which comes about when linearly polarized emission from the far side of the jet is partially converted to circularly polarized emission as it passes through the magnetized plasma at the front side of the jet on its way towards the observer. When both of these properties are manifest, they can be used jointly with the jet linear polarization structure to uniquely determine both the direction of B p and the direction of the central rotation. This technique has been applied to 12 AGNs. The results indicate statistically equal numbers of outward and inward B p and of clockwise (CW) and counter-clockwise (CCW) rotations of the central black holes on the sky. However, they suggest that the directions of B p and of the central rotation are coupled: CW/CCW central rotation is preferentially associated with inward/outward poloidal B field. This leads to a preferred orientation for the toroidal B-field component corresponding to inward current along the jet. View Full-Text
Keywords: active galactic nuclei; relativistic jets; magnetic fields; radio interferometry active galactic nuclei; relativistic jets; magnetic fields; radio interferometry
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Gabuzda, D. Determining the Jet Poloidal B Field and Black-Hole Rotation Directions in AGNs. Galaxies 2018, 6, 9.

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