Evolution of the grain size distribution in Milky Way-like galaxies in post-processed IllustrisTNG simulations

Abstract

ABSTRACT We model dust evolution in Milky Way-like galaxies by post-processing the IllustrisTNG cosmological hydrodynamical simulations in order to predict dust-to-gas ratios and grain size distributions. We treat grain-size-dependent dust growth and destruction processes using a 64-bin discrete grain size evolution model without spatially resolving each galaxy. Our model broadly reproduces the observed dust–metallicity scaling relation in nearby galaxies. The grain size distribution is dominated by large grains at z ≳ 3 and the small-grain abundance rapidly increases by shattering and accretion (dust growth) at z ≲ 2. The grain size distribution approaches the so-called MRN distribution at z ∼ 1, but a suppression of large-grain abundances occurs at z < 1. Based on the computed grain size distributions and grain compositions, we also calculate the evolution of the extinction curve for each Milky Way analogue. Extinction curves are initially flat at z > 2, and become consistent with the Milky Way extinction curve at z ≲ 1 at $1/\lambda \lt 6~\rm{\mu m}^{-1}$. However, typical extinction curves predicted by our model have a steeper slope at short wavelengths than is observed in the Milky Way. This is due to the low-redshift decline of gas-phase metallicity and the dense gas fraction in our TNG Milky Way analogues that suppresses the formation of large grains through coagulation.