Stacked integrated spectra for the different QSOs subgroups A, B, C, D (properties of the individual samples are indicated in the top labels). For each plot, the first panel from top shows the [CII] flux density as a function of velocity, in bins of 60 km s⁻¹. The red curve represents the best-fit 2 Gaussian components model; the two individual components are shown with blue and green curves. Labels indicate the number of stacked sources and the luminosity of the broad [CII] wings. The inset shows a zoom on the broad component. Second panel from top: residuals from the subtraction of the core component (blue line in first panel). The green curve shows the best fit broad component. Third panel: residuals from the two Gaussian components fitting. The 1σ rms of the spectrum is also indicated by the shaded region.