Velocity dispersion gradient inside 0.15 × r₉₀ for high- and low-n_b galaxies. The blue box marks the interquartile range of the sample, the black line in the box gives the median value. The top and bottom black line stand for the highest and lowest value, respectively. The thick green line at ∇σ = −0.18 gives a good demarcation to separate the subsamples based on the velocity dispersion gradient.