Normalised residuals of galaxy velocity about the mean scaling relation in the fiducial analysis. Red points show the data and the black line is the model, Eq. (4), a mixture of a Gaussian and a uniform distribution. Error bars are calculated by bootstrapping the velocities of the spectroscopic sample, using 64 bins between − 4 and 4 in v_gal ∕σ_gal. See text for discussion of the goodness of fit.