Plot of 500 random stacks from the bootstrapping in grey. The stacks are from the same sample of 16 224 cluster–quasar pairs stacked at randomised redshifts from the full redshift distribution. The overlayed black dotted line represents the median flux per velocity bin of the 500 random stacks. On top, we over-plot in red the original blind stack from Fig. 8 to illustrate the difference.