Left panel: Inferred X_CO conversion factor from Eq. (8) as a function of τ₁₆₀. Also shown are values that would be estimated from the metallicity dependence found by Hunt et al. (2020) as X_CO ∝ Z^−1.55 (see also Accurso et al. 2017). Heavy curves show the medians in log₁₀(τ₁₆₀) for each galaxy (except for NGC 1705 for which there are too few points), and the shaded regions indicate 1σ standard deviations. Right panel: GDR (here we are using the inverse of δ_DGR) that would be inferred assuming the metallicity dependence of the X_CO conversion factor found by Hunt et al. (2020). The range of GDRs estimated by different methods is shown as the hatched horizontal strips. As in the left panel, heavy curves show the medians, and shaded regions the 1σ standard deviation.