Comparisons between the different criteria for selecting QGs. Upper panel: Distributions of M_dust/M_⋆, Δ_MS and stellar age for our parent sample (solid black line) against the samples satisfying additional criteria of quiescence: UVJ selection proposed in Muzzin et al. (2013) (dark red line) and D_n4000 > 1.6 (orange line). Lower panel (left:) Positions of 545 dusty QGs from this work in the UVJ rest-frame colour plane. Regions defined with solid and dashed lines correspond to the criteria indicated in the legend. Coloured circles represent QGs with 1.5 < D_n4000 < 1.6 and can be considered potential contaminants; (right:) Evolution of specific dust mass as a function of M_⋆. The meanings of the symbols are the same as in the left panel. Best linear fits are shown for eQGs and sQGs for two different cases: the main selection that includes 545 QGs (dark grey lines) and the selection that fulfils the stricter spectroscopic criterion D_n4000 > 1.6 (salmon coloured lines).