Stellar Migration and Chemical Enrichment in the Milky Way Disc: A
  Hybrid Model
  We develop a hybrid model of galactic chemical evolution that combines a
multi-ring computation of chemical enrichment with a prescription for stellar
migration and the vertical distribution of stellar populations informed by a
cosmological hydrodynamic disc galaxy simulation. Our fiducial model adopts
empirically motivated forms of the star formation law and star formation
history, with a gradient in outflow mass loading tuned to reproduce the
observed metallicity gradient. With this approach, the model reproduces many of
the striking qualitative features of the Milky Way disc's abundance structure:
(i) the dependence of the [O/Fe]-[Fe/H] distribution on radius $R_\text{gal}$
and midplane distance $|z|$; (ii) the changing shapes of the [O/H] and [Fe/H]
distributions with $R_\text{gal}$ and $|z|$; (iii) a broad distribution of
[O/Fe] at sub-solar metallicity and changes in the [O/Fe] distribution with
$R_\text{gal}$, $|z|$, and [Fe/H]; (iv) a tight correlation between [O/Fe] and
stellar age for [O/Fe] $>$ 0.1; (v) a population of young and intermediate-age
$\alpha$-enhanced stars caused by migration-induced variability in the Type Ia
supernova rate; (vi) non-monotonic age-[O/H] and age-[Fe/H] relations, with
large scatter and a median age of $\sim$4 Gyr near solar metallicity.
Observationally motivated models with an enhanced star formation rate $\sim$2
Gyr ago improve agreement with the observed age-[Fe/H] and age-[O/H] relations,
but worsen agreement with the observed age-[O/Fe] relation. None of our models
predict an [O/Fe] distribution with the distinct bimodality seen in the
observations, suggesting that more dramatic evolutionary pathways are required.
All code and tables used for our models are publicly available through the
Versatile Integrator for Chemical Evolution (VICE;
https://pypi.org/project/vice).
