Halo line-of-sight velocity dispersion vs. halo mass, for lightcones from the GAEA semi-analytical model (without orphan galaxies, blue circles, 7 deg²) and for Flagship (red stars, here for the 49 deg² region), at three representative redshifts. The lines are simple non-theoretical representations. While Flagship uses virial quantities, GAEA uses R_200c for the virial radius and therefore the x axis is log10[M_200c/(h⁻¹ M_⊙)] for GAEA. Only haloes with at least 10 member galaxies with I_E < 24.5 and H_E < 24 within the virial cylinder are considered, with at least 10 such haloes per mass bin. The velocity dispersions are measured with the gapper method (Wainer & Thissen 1976), and the error bars assume Gaussian velocity distributions, i.e., $ϵ(\sigma )=\sigma /\sqrt{2(N-1)}$, where N is the number of galaxies per mass bin.