Comparison of the BTFR to the MOND prediction. Datapoints with errorbars are the galaxies in the α.btfr sample, color-coded by the kurtosis of their HI profile (same as in Fig. 6). The two yellow solid lines represent the MOND prediction for the BTFR (Milgrom 1983a), for two values of the theory’s acceleration parameter, α₀ (indicative of the parameter’s measurement uncertainty; see Sect. 5.4 for details). MOND further predicts that the BTFR is a perfect power-law, i.e., it predicts a relation with zero intrinsic scatter. Keep in mind that the MOND prediction refers to asymptotic flat velocities (V_rot=V_flat), while rotational velocities for α.btfr galaxies are linewidth-derived values (V_rot= W/ 2).