B-band absolute magnitude M_B as a function of redshift. The red and blue solid lines mark the absolute magnitude of the principal and the companion galaxy, respectively, at redshifts with PDF (z) > 0. The letter in each panel refers to the companion galaxy in Fig. 4. The dark grey area marks the selection of the primary sample, and the two grey areas mark the selection of the secondary sample (i.e., the primary sample is included in the secondary one). The vertical dashed lines mark the redshift range under study, 0.4 ≤ z< 1. The redshifts at which the pair selection mask ℳ^pair is equal to one are marked with the thick green line. (Colour version online.)