Centroid velocity distributions of the one- and two-velocity-components fits. The black histogram represents the centroid velocity distribution of the spectra fit by the one-velocity-component model. The blue and red histograms show the centroid velocity distributions of the spectra fit with the two-velocity-components model, where blue corresponds to the first velocity component and red to the second velocity component. The solid black line represents the middle point X located at 0.025 km s⁻¹, measured via Eq. (1) (see text). This divides the black histogram into two velocities, as explained in Sect. 3.4.