Notes. Parameters in the disk and halo used by Shneider et al. (2014a) to model the degree of polarization as a function of wavelength in the example region “A” in M 51, located in the radial ring 2.4 − 3.6 kpc and centered at the azimuthal angle of 100°. Fixed parameters were: the electron densities n_e and path lengths L (adopted from Berkhuijsen et al. 1997), the turbulence cell size d (computed using Eq. (5) with the given parameter values), the number density of CREs (in arbitrary units; its value is not relevant since it cancels out when calculating the depolarization (p/p₀)), and the degree of anisotropy α of the turbulent field (α = 1 meaning a purely isotropic field). The values of the regular and turbulent magnetic field strengths B and b (assumed to be constant along azimuthal angle in the radial ring) were chosen in Shneider et al. (2014a) to be consistent with the observed degrees of polarization p available at that time.