Diffusion models with an energy-dependent diffusion coefficient [D(E) = D₀(E/1 GeV)^μ] for NGC 4565 (assuming μ = 0.3). Data points denote the vertical profile of the non-thermal spectral index between 1.5 and 6 GHz (left panels) and the Gaussian model of the non-thermal intensity profile at 1.5 GHz (right panels). The radial position of each profile is given in the right-hand-side plot; r <  0 is east of the minor axis and r >  0 is west of the minor axis. Positive z values are on the north side and negative ones on the south side of the mid-plane. Solid lines show the best-fitting diffusion models.