Derivation of ¹²CO(1−0) luminosity. Upper panels: Comparison between the values of derived from ¹²CO transitions (2 − 1), (3 − 2), (4 − 3) and (5 − 4) adopting the SMGs line luminosity ratios from Carilli & Walter (2013). Bottom panel: Values of derived from the lowest- transition available (up to 5 − 4), compared to those computed as the average of values from all available ¹²CO transitions from (2 − 1) to (5 − 4). The colour coding specifies which is the lowest J_up available and indicates the typical uncertainties involved. The solid red line shows the 1:1 locus.