Comparison between the width, corrected for the instrumental resolution, of the [Mg IV] and Hu-12 lines (top) and between the velocity shifts of [Mg IV] and the broad Pf-γ component relative to the narrow Pf-γ component (bottom). The symbols are as in Fig. 3. The large blue star in the top panel represents the mean σ_corr in each axis. The solid black line is the one-to-one relation. The shaded blue and red areas in the bottom panel indicate blue and red velocity shifts, respectively.