Results from spectral stacking. From left to right, the stacked spectrum corresponds to the median values, 3σ-clipped mean and weighted mean. The long red segment shows the DLA core region over which τ > 6 for log  N(H i) ≥ 21.7, ensuring no residual flux from the quasar. This region is highlighted in the inset panels. The short red segment (inner tick marks) indicates the 1000 km s^-1 central region over which the Ly α luminosity is integrated. The green spectrum is the composite Lyman-break galaxy spectrum from Shapley et al. (2003), scaled to match the same luminosity in the Ly α region.