The Galactic Dust-Up: Modeling Dust Evolution in FIRE
  Recent strides have been made developing dust evolution models for galaxy
formation simulations but these approaches vary in their assumptions and degree
of complexity. Here we introduce and compare two separate dust evolution models
(labelled 'Elemental' and 'Species'), based on recent approaches, incorporated
into the GIZMO code and coupled with FIRE-2 stellar feedback and ISM physics.
Both models account for turbulent dust diffusion, stellar production of dust,
dust growth via gas-dust accretion, and dust destruction from time-resolved
supernovae, thermal sputtering in hot gas, and astration. The "Elemental" model
tracks the evolution of generalized dust species and utilizes a simple,
'tunable' dust growth routine, while the "Species" model tracks the evolution
of specific dust species with set chemical compositions and incorporates a
physically motivated, two-phase dust growth routine. We test and compare these
models in an idealized Milky Way-mass galaxy and find that while both produce
reasonable galaxy-integrated dust-to-metals (D/Z) ratios and predict gas-dust
accretion as the main dust growth mechanism, a chemically motivated model is
needed to reproduce the observed scaling relation between individual element
depletions and D/Z with column density and local gas density. We also find the
inclusion of theoretical metallic iron and O-bearing dust species are needed in
the case of specific dust species in order to match observations of O and Fe
depletions, and the integration of a sub-resolution dense molecular gas/CO
scheme is needed to both match observed C depletions and ensure carbonaceous
dust is not overproduced in dense environments.
