Asymmetry of the blue and red Lyα peaks in the GP sample, measured from (panel a) the systemic redshift, and (panel b) the central trough. Panel a also includes the mean positions of the blue and red peaks for this GP sample, and for LAE and LBG samples drawn from the literature (Hashimoto et al. 2015). The GPs are similar to the LAEs in the red peak positions, but have a smaller mean blue offset.