Evolution of dust-to-metal ratio in galaxies

This paper investigates the evolution of the dust-to-metal ratio in galaxies based on a simple evolution model for the amount of metal and dust with infall. We take into account grain formation in stellar mass-loss gas, grain urowth bv the accretion of metallic atoms in a cold dense cloud, and grain destruction by SN shocks. Especially, we propose that the accretion efficiency is independent of the star-formation history. This predicts various evolutionary tracks in the metallicity (Z)-dust-to-gas ratio (D) plane depending on the star-formation history. In this framework, the observed linear Z-D relation of nearby spiral galaxies can be interpreted as a sequence of a constant galactic age. We emphasize that an observational study of the Z-D relation of galaxies at z similar to 1 is very useful to constrain the efficiencies of dust growth and destruction. We also suggest that the Lyman break galaxies at z similar to 3 have a very low dust-to-metal ratio, typically less than or similar to 0.1. Although the effect of infall on the evolutionary tracks in the Z-D plane is quite small. the dispersion of the infall rate can disturb the Z-D relation with a constant galactic age.