Dominance of outflowing electric currents on decaparsec to kiloparsec scales in extragalactic jets

TL;DR

This paper presents observational evidence supporting a nested helical magnetic-field structure in extragalactic jets, consistent with the Cosmic Battery model, revealing dominant outflowing electric currents on large scales.

Contribution

It provides new observational evidence for the Cosmic Battery's predicted magnetic field structure and current directions in AGN jets across different scales.

Findings

Inward axial current on parsec scales inferred from FR gradients.

Outward current on kiloparsec scales consistent with jet sheath or disk wind.

Support for the Cosmic Battery mechanism in AGN jet magnetic field generation.

Abstract

Helical magnetic fields embedded in the jets of active galactic nuclei (AGNs) are required by the broad range of theoretical models that advocate for electromagnetic launching of the jets. In most models, the direction of the magnetic field is random, but if the axial field is generated by a Cosmic Battery generated by current in the direction of rotation in the accretion disk, there is a correlation between the directions of the spin of the AGN accretion disk and of the axial field, which leads to a specific direction for the axial electric current, azimuthal magnetic field, and the resulting observed transverse Faraday-rotation (FR) gradient across the jet, due to the systematic change in the line-of-sight magnetic field. We consider new observational evidence for the presence of a nested helical magnetic-field structure such as would be brought about by the operation of the Cosmic Battery, and make predictions about the expected behavior of transverse FR gradients observed on decaparsec and kiloparsec scales. The collected results can be understood if the dominant azimuthal field on parsec scales corresponds to an axial electric current flowing inward along the jet, whereas the (weaker) dominant azimuthal field on kiloparsec scales corresponds to a outward-flowing current in the outer sheath of the jet and/or an extended disk wind.