Top panel: stacked spectra with geometric mean, bottom panel: arithmetic mean. As in Fig. 2, we plot the observed spectrum (thick solid line), the modelled spectrum (dotted line), the host galaxy spectrum (thin solid line), the power-law contribution (dotted line), and the residual spectra (lower panel). The observed spectra is normalised at the flux value in λ = 4020. Bottom panel: same as top panel, but is zoomed in on the blue part of the spectra.