Faraday rotation and the turbulent structure of the Galaxy

Abstract

We extend Jokipii and Lerche's analysis of the turbulent structure of our Galaxy by means of a study of the rotation measure of extragalactic sources. Like them we use a simple, statistically homogeneous and isotropic disc model of the Galaxy and assume that the magnetic field has both an average component and a fluctuating one. We assume that the electron density is proportional to some power of the magnetic field (NeαBn with 1≤n≤2). Using the rotation measure data on 242 extragalactic sources given by Vallee and Kronberg we consider both an exponential and a Gaussian two-point correlation function for the (Gaussian) fluctuating component of the magnetic field with a correlation lengthL. We find reasonable agreement between theory and observations for an average magnetic field of about 3 μG, a fluctuating magnetic field component with an amplitude of about 2.6μG, an average electron density of about 0.03 cm−3, a fluctuating density component of about 0.05 cm−3, and a correlation length of about 300 pc.