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Galaxies 2017, 5(1), 11; doi:10.3390/galaxies5010011

The Origin and Structure of the Magnetic Fields and Currents of AGN Jets

Physics Department, University College Cork, Cork, Ireland
Received: 17 October 2016 / Accepted: 3 January 2017 / Published: 2 February 2017
(This article belongs to the Special Issue Blazars through Sharp Multi-wavelength Eyes)
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Simple Summary

active galactic nuclei; relativistic jets; magnetic fields; radio interferometry

Abstract

This paper reviews observational evidence obtained to date about the overall structure of the magnetic fields in the jets of Active Galactic Nuclei (AGN). Because they are sensitive to the line-of-sight magnetic-field component, Faraday rotation observations of AGN jets provide an effective tool for searching for toroidal jet magnetic fields, whose line-of-sight component changes systematically across the jet. Transverse Faraday rotation measure (RM) gradients providing direct evidence for helical/toroidal magnetic fields have been reliably detected in nearly 40 AGN on parsec scales. Helical magnetic fields are believed to form due to the combined action of the rotation of the central black hole and accretion disk, and these observations demonstrate that at least some of this helical field survives to distances well beyond the Very Long Baseline Interferometry (VLBI) core. Observations of reversals in the direction of the transverse RM gradients in a number of AGN provide evidence for a“return”magnetic field forming a nested helical-field structure with oppositely directed azimuthal components in the inner and outer regions of the helical magnetic field. The collected data now provide firm evidence for a predominance of inward jet currents on parsec scales and outward currents on scales greater than a few tens of parsecs. This suggests a global pattern of magnetic fields and currents with an inward current near the jet axis and an outward current farther from the jet axis, with these currents closing in the accretion disk and far out in the radio lobes, forming a self-consistent set of fields and currents together with the implied nested helical-field structure. 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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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Gabuzda, D. The Origin and Structure of the Magnetic Fields and Currents of AGN Jets. Galaxies 2017, 5, 11.

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