Top: M_BB/M_star as a function of metallicity for DGS (purple crosses) and KINGFISH (orange downward triangles). The best power-law fit is indicated as a black line, and corresponds to: log (M_BB/M_star) = (−21.8 ± 1.5) + (20.3 ± 1.6) × log (12 + log (O/H)). The distribution of M_BB/M_star is indicated on the side for both samples: plain purple line for DGS and dashed orange line for KINGFISH. Bottom: L_FIR/M_BB as a function of metallicity for DGS (crosses) and KINGFISH (downward triangles). The colours code the temperature, T. The best power-law fit line is indicated as a black line, and corresponds to: log (L_FIR/M_BB) = (24.4 ± 1.1) + (−23.6 ± 1.2) × log (12 + log (O/H)). The distribution of L_FIR/M_BB is indicated on the side for both samples: plain line for DGS and dashed line for KINGFISH. On both plots: the errors on the metallicities are omitted for clarity. They are of about 0.1 dex on average.