Scatter plots of the radial velocity vs. the self-gravitational potential (top two panels), and scatter plots of the radial velocity vs. mutual gravitational potential (bottom two panels). The blue lines in all four panels represent the fitting lines of the square of velocity and gravitational potential, and the red scatter points indicate the regions in which M_line > 2000 M_⊙ pc⁻¹. The Pearson correlation coefficients (r) and corresponding p-values between velocity squared and gravitational potential are shown in the bottom left corner of each panel.