Dust-to-gas mass ratio as a function of metallicity. Purple triangles indicate the 3σ lower limits from [C I](³P₂−³P₁) under high- and low-excitation conditions. The gold and blue stars indicate M_gas from [C II] using the conversions in Zanella et al. (2018) and Heintz et al. (2021), respectively. The red star shows the maximum amount of gas allowed by [C II] dynamics (F21). The points are slightly offset along the X axis for clarity. The uncertainty on the metallicity is represented by the horizontal red bar. The blue lines mark the (extrapolated) relations from Magdis et al. (2012), Rémy-Ruyer et al. (2014), De Vis et al. (2019), Popping & Péroux (2022), and Popping et al. (2023), and the models from Mauerhofer & Dayal (2023), Popping et al. (2017), Li et al. (2019), and Vijayan et al. (2019).