AGN Jets and Winds in Polarised Light: The Case of Mrk 231

TL;DR

This study uses multi-frequency radio polarimetric observations to reveal a complex, magnetized outflow structure in Mrk 231, including a weakly collimated jet and surrounding wind, providing insights into AGN feedback mechanisms.

Contribution

It presents detailed polarimetric imaging of Mrk 231, demonstrating the presence of a broad, magnetized outflow with a jet and wind structure, and estimates the jet production efficiency.

Findings

Detection of a broad, curved outflow with a weakly collimated jet

Magnetic fields inferred as poloidal in the jet and toroidal in the wind

Jet production efficiency estimated at approximately 1%

Abstract

We present the results of a multi-frequency, multi-scale radio polarimetric study with the Very Large Array (VLA) of the Seyfert 1 galaxy and BALQSO, Mrk 231. We detect complex total and polarized intensity features in the source. Overall, the images indicate the presence of a broad, one-sided, curved outflow towards the south which consists of a weakly collimated jet with poloidal inferred magnetic fields, inside a broader magnetized ``wind'' or ``sheath'' component with toroidal inferred magnetic fields. The model of a kpc-scale weakly collimated jet/lobe in Mrk 231 is strengthened by its C-shaped morphology, steep spectral index throughout, complexities in the magnetic field structures, and the presence of self-similar structures observed on the 10-parsec-scale in the literature. The ``wind'' may comprise both nuclear starburst (close to the core) and AGN winds, where the latter maybe the primary contributor. Moving away from the core, the ``wind'' component may also comprise the outer layers (or ``sheath'') of a broadened jet. The inferred value of the (weakly collimated) jet production efficiency, $\eta_\mathrm{jet}\sim$0.01 is consistent with the estimates in the literature. The composite jet and wind outflow in Mrk 231 appears to be low-power and matter-dominated, and oriented at a small angle to our line of sight.