Magnetic-field fluctuations around the radio galaxy 3C 31

TL;DR

This paper analyzes magnetic-field fluctuations around radio galaxy 3C 31 using rotation measure data, revealing a foreground medium with a power-law turbulence spectrum and a cavity created by the source.

Contribution

It provides the first detailed RM structure function analysis and 3D simulations linking magnetic turbulence to the galaxy's environment and cavity formation.

Findings

RM fluctuations are primarily due to a foreground medium.

The power spectrum of magnetic turbulence follows a power law with a cutoff.

The RM distribution aligns with a spherical plasma cavity around 3C 31.

Abstract

We present an analysis of the magnetic-field fluctuations in the magnetoionic medium in front of the radio galaxy 3C 31 derived from rotation-measure (RM) fits to high-resolution polarization images. We first show that the Faraday rotation must be due primarily to a foreground medium. We determine the RM structure functions for different parts of the source and infer that the simplest form for the power spectrum is a power law with a high-frequency cutoff. We also present three-dimensional simulations of RM produced by a tangled magnetic field in the hot plasma surrounding 3C 31, and show that the observed RM distribution is consistent with a spherical plasma distribution in which the radio source has produced a cavity.