Galaxies with grains: unraveling dust evolution and extinction curves with hydrodynamical simulations
arxiv(2024)
摘要
We introduce a model for dust evolution in the ramses code for
simulations of galaxies with a resolved multiphase interstellar medium. Dust is
modelled as a fluid transported with the gas component, and is decomposed into
two sizes, 5 nm and 0.1 μ m, and two chemical compositions for
carbonaceous and silicate grains. Using a suite of isolated disc simulations
with different masses and metallicities, the simulations can explore the role
of these processes in shaping the key properties of dust in galaxies. The
simulated Milky Way analogue reproduces the dust-to-metal mass ratio, depletion
factors, size distribution and extinction curves of the Milky Way. Galaxies
with lower metallicities reproduce the observed decrease in the dust-to-metal
mass ratio with metallicity at around a few 0.1 Z_⊙. This break in
the DTM corresponds to a galactic gas metallicity threshold that marks the
transition from an ejecta-dominated to an accretion-dominated grain growth, and
that is different for silicate and carbonaceous grains, with ≃0.1
Z_⊙ and ≃ 0.5 Z_⊙ respectively. This leads to more
Magellanic Cloud-like extinction curves, with steeper slopes in the ultraviolet
and a weaker bump feature at 217.5 nm, in galaxies with lower masses and lower
metallicities. Steeper slopes in these galaxies are caused by the combination
of the higher efficiency of gas accretion by silicate relative to carbonaceous
grains, and by the low rates of coagulation that preserves the amount of small
silicate grains. Weak bumps are due to the overall inefficient accretion growth
of carbonaceous dust at low metallicity, whose growth is mostly supported by
the release of large grains in SN ejecta. We also show that the formation of CO
molecules is a key component to limit the ability of carbonaceous dust to grow,
in particular in low-metallicity gas-rich galaxies.
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