MODELING DUST EVOLUTION IN GALAXIES WITH A MULTIPHASE, INHOMOGENEOUS ISM

Abstract

ABSTRACT We develop a model of dust evolution in a multiphase, inhomogeneous interstellar medium (ISM) using hydrodynamical simulations of giant molecular clouds in a Milky Way–like spiral galaxy. We improve the treatment of dust growth by accretion in the ISM to investigate the role of the temperature-dependent sticking coefficient and ion–grain interactions. From detailed observational data on the gas-phase Si abundances measured in the local Galaxy, we derive a relation between the average and the local gas density that we use as a critical constraint for the models. This relation requires a sticking coefficient that decreases with the gas temperature. The relation predicted by the models reproduces the slope of −0.5 for the observed relation in cold clouds, which is steeper than that for the warm medium and is explained by dust growth. We find that growth occurs in the cold medium for all adopted values of the minimum grain size a min from 1 to 5 nm. For the classical cutoff of , the Coulomb repulsion results in slower accretion and higher than the observed values. For , the Coulomb interactions enhance the growth rate, steepen the slope of the – relation, and provide a better match to observations. The rates of dust re-formation in the ISM by far exceed the rates of dust production by stellar sources. After the initial 140 Myr, the cycle of matter in and out of dust reaches a steady state, in which the dust growth balances the destruction on a similar timescale of 350 Myr.