The Evolution of the Elemental Abundances in the Gas and Dust Phases of the Galaxy

Abstract

We present models for the evolution of the elemental abundances in the gas and dust phases of the interstellar medium (ISM) of our Galaxy by generalizing standard models for its dynamical and chemical evolution. In these models, the stellar birthrate history is determined by the infall rate of primordial gas, and by its functional dependence on the mass surface density of the stars and gas. We adopt a two component model for the Galaxy, consisting of a central bulge and an exponential disk with different infall rates and stellar birthrate histories. Condensation in stellar winds, Type Ia and Type II supernovae, and the accretion of refractory elements onto preexisting grains in dense molecular clouds are the dominant contributors to the abundance of elements locked up in the dust. Grain destruction by sputtering and evaporative grain-grain collisions in supernova remnants are the most important mechanisms that return these elements back to the gas phase. We calculate the dust production rate by the various dust sources, analyze the origin of the elemental depletion pattern, and study the relation between dust abundance and ISM metallicity, and the evolution of the the dust abundance and composition at each Galactocentric radius as a function of time. The derived relation of dust mass with metallicity is compared to the observed Galactic dust abundance gradient, and to the M$_{dust}$ versus log(O/H) relation that is observed in external Dwarf galaxies. The dependence of dust composition on the mass of the progenitor star, and the delayed recycling of newly synthesized dust by low mass stars back to the ISM give rise to variations in the dust composition as a function of time. Our models provide a framework for the self-consistent inclusion of dust in