Evidence of internal rotation and a helical magnetic field in the jet of the quasar NRAO150

TL;DR

This paper presents multi-epoch VLBI observations of quasar NRAO150, revealing internal jet rotation and a helical magnetic field, supporting a model where the jet is viewed nearly face-on with rotating emission regions.

Contribution

It provides new polarimetric VLBI data and a helical jet model that demonstrate internal rotation and magnetic field structure in NRAO150's jet, advancing understanding of jet dynamics.

Findings

Detection of toroidal magnetic field component in the jet

Evidence of high-speed internal rotation of jet regions

Support for a helical magnetic field and face-on jet orientation

Abstract

The source NRAO150 is a very prominent millimeter to radio emitting quasar at redshift z=1.52 for which previous millimeter VLBI observations revealed a fast counterclockwise rotation of the innermost regions of the jet. Here we present new polarimetric multi-epoch VLBI-imaging observations of NRAO150 performed at 8, 15, 22, 43, and 86GHz with the VLBA and GMVA between 2006 and 2010. All new and previous observational evidence are consistent with an interpretation of the source behavior where the jet is seen at an extremely small angle to the line of sight, and the high frequency emitting regions in NRAO150 rotate at high speeds on the plane of the sky with respect to a reference point that does not need to be related to any particularly prominent jet feature. The observed polarization angle distribution at 22, 43, and 86 GHz during observing epochs with high polarization degree suggests that we have detected the toroidal component of the magnetic field threading the innermost jet plasma regions. This is also consistent with the lower degree of polarization detected at progressively poorer angular resolutions, where the integrated polarization intensity produced by the toroidal field is explained by polarization cancellation inside the observing beam. All this evidence is fully consistent with a kinematic scenario where the main kinematic and polarization properties of the 43 GHz emitting structure of NRAO150 are explained by the internal rotation of such emission regions around the jet axis when the jet is seen almost face on. A simplified model developed to fit helical trajectories to the observed kinematics of the 43 GHz features fully supports this hypothesis. This explains the kinematics of the innermost regions of the jet in NRAO150 in terms of internal jet rotation.