Linear polarization in the nucleus of M87 at 7 mm and 1.3 cm

TL;DR

This study presents high-resolution polarimetric images of M87's nucleus at 7 mm and 1.3 cm, revealing stable polarization structures over 11 years and insights into magnetic fields and Faraday rotation in the galaxy's core.

Contribution

First detailed multi-epoch polarimetric imaging of M87's nucleus at these wavelengths, showing long-term stability and magnetic field implications.

Findings

Stable polarization pattern over 11 years

Detection of small month-scale variability

Evidence for magnetic structure in the MHD wind

Abstract

We report on high angular resolution polarimetric observations of the nearby radio galaxy M87 using the Very Long Baseline Array at 24 GHz ($\lambda=$1.3 cm) and 43 GHz ($\lambda=$7 mm) in 2017-2018. New images of the linear polarization substructure in the nuclear region are presented, characterized by a two-component pattern of polarized intensity and smooth rotation of the polarization plane around the 43 GHz core. From a comparison with an analogous dataset from 2007, we find that this global polarization pattern remains stable on a time interval of 11 yr, while showing smaller month-scale variability. We discuss the possible Faraday rotation toward the M87 nucleus at centimeter to millimeter wavelengths. These results can be interpreted in a scenario where the observed polarimetric pattern is associated with the magnetic structure in the confining magnetohydrodynamic wind, which also serves as the source of the observed Faraday rotation.