Faraday rotation and the turbulent structure of the Galaxy

The authors extend Jokipii and Lerche's analysis of the turbulent structure of the Galaxy by means of a study of the rotation measure of extragalactic sources. Like them a simple, statistically homogeneous and isotropic disc model of the Galaxy is used and it is assumed that the magnetic field has both an average component and a fluctuating one. It is assumed that the electron density is proportional to some power of the magnetic field (Nsub(e)αBsup(n) with 1<=n<=2). Using the rotation measure data on 242 extragalactic sources given by Vallee and Kronberg both an exponential and a Gaussian two-point correlation function are considered for the (Gaussian) fluctuating component of the magnetic field with a correlation length L. Reasonable agreement between theory and observations is found for an average magnetic field of about 3 μG, a fluctuating magnetic field component with an amplitude of about 2.6 μG, 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. (Auth.)