Surface density of SNRs and candidates in M 31 (this work) and M 33 (Long et al. 2010) plotted over the radius normalised to D₂₅/2 (D₂₅ = 155.5′, 52.6′ for M 31 and M 33, respectively, de Vaucouleurs et al. 1991). The radial distance in kpc is given along the upper x-axis. Dotted lines show the fitted model function f(x) = Cx^αexp( − βx), dashed lines show the model function for the Milky Way normalised to the maximum of M 31 or M 33.