Correlation between FIR and CO luminosities, for our sample (filled black circles, and arrows for upper limits) and other galaxies from the literature (same symbols as in Fig. 6). The 3 lines are for L_FIR/M(H₂) = 10, 100 and 1000 L_⊙/M_⊙  from bottom to top, assuming a conversion factor α = 0.8   M_⊙ (Kkms^-1  pc²)^-1. The same lines correspond to gas depletion time scales of 580 (bottom), 58 (middle) and 5.8 Myr (top). The arrows indicate the direction and amount by which these lines would move if the Milky Way CO-to-H₂  conversion factor was used.