Upper panel: spectra of the six QSOs if our sample. Each spectrum is extracted from a nuclear region of 0.25′′× 025′′ (2 × 2 pixel). The different components in the fit for each line (Hβ, [Oiii] and FeII) are shown in green, and the red line is the total fit. The shaded yellow regions indicate the zone affected by strong sky-line residuals that are excluded from the fit. Lower panel: fit residuals, obtained as a difference between observed and model spectra.