Asymmetry of the red peak of the Lyman α line (asymmetry parameter a_asym. in Eq. (3)) compared to the peak separation, colour-coded by the logarithmic EW₀. As in Fig. 14, coloured dots with black circles show objects without UV continuum counterparts. The grey cross in the top left corner shows the median errors. The black dots and error bars show the median asymmetry (including lower limits) in peak separation bins. The x-axis error bars show the widths of the bins, the y-axis error bars show the first and last quartiles. The asymmetry is defined such that positive values mean the line has a red wing, while negative values mean the line has a blue wing (and zero means no asymmetry, shown as the dashed grey line).