Stacks of the z ∼ 6 and z ∼ 7 sources (in blue and red respectively) showing a very asymmetric Lyα line in both cases: the z ∼ 6 stacked line is broader than the higher-redshift line. The dashed green line is the resolution of the FORS2 spectra. We also note the positive continuum redward of the line for the z ∼ 6 stack, while in the z ∼ 7 case the flux is consistent with the noise. In the inset, the Lyα line from the stacks, with the lower-redshift sample split into two bins (5.5–6 in blue and 6–6.5 in green), which are consistent with each other.