Angular separation θ as a function of redshift. The solid lines mark the measured angular separation of the close pairs, θ = 7.36″ in panel a) and θ = 10.46″ in panel b). The letter in each panel refers to the companion galaxy in Fig. 4. The grey area marks the angular separations between θ_min (z) and θ_max (z) (red dashed lines). The vertical dashed lines mark the redshift range under study, 0.4 ≤ z< 1. The redshifts at which the angular mask ℳ^θ is equal to one are marked with the thick green line.