2022ApJ...935..105R

The evolution of the metal content of the universe can be tracked through rest-frame UV spectroscopy of damped Lyα systems (DLAs). Gas-phase abundances in DLAs must be corrected for dust depletion effects, which can be accomplished by calibrating the relation between abundance ratios such as [Zn/Fe] and depletions (the fraction of metals in gas, as opposed to dust). Using samples of gas-phase abundances and depletions in the Milky Way (MW), LMC, and SMC, we demonstrate that the relation between [Zn/Fe] and other abundance ratios does not change significantly between these local galaxies and DLAs, indicating that [Zn/Fe] should trace depletions of heavy elements in those systems. The availability of photospheric abundances in young massive stars, a proxy for the total (gas+dust) metallicity of neutral gas, in the MW, LMC, and SMC allows us to calibrate the relation between [Zn/Fe] and depletions in these nearby galaxies. We apply the local calibrations of depletions to DLAs. We find that the fraction of metals in dust, the dust-to-gas ratio, and total abundances are 2-5 times lower than inferred from previous depletion calibrations based on MW measurements and a different formalism. However, the trend of dust abundance versus metallicity remains only slightly sublinear for all existing depletion calibrations, contrary to what is inferred from far-IR (FIR), 21 cm, and CO emission in nearby galaxies and predicted by chemical evolution models. Observational constraints on the FIR dust opacity and depletions at metallicities lower than 20% solar will be needed to resolve this tension.