Stellar migrations and metal flows -- Chemical evolution of the thin
  disc of a simulated Milky Way analogous galaxy
  In order to understand the roles of metal flows in galaxy formation and
evolution, we analyse our self-consistent cosmological chemo-dynamical
simulation of a Milky Way like galaxy during its thin-disc phase. Our simulated
galaxy disc qualitatively reproduces the variation of the dichotomy in
[$\alpha$/Fe]-[Fe/H] at different Galactocentric distances as derived by
APOGEE-DR16, as well as the stellar age distribution in [$\alpha$/Fe]-[Fe/H]
from APOKASC-2. The disc grows from the inside out, with a radial gradient in
the star-formation rate during the entire phase. Despite the radial dependence,
the outflow-to-infall ratio of metals in our simulated halo shows a
time-independent profile scaling with the disc growth. The simulated disc
undergoes two modes of gas inflow: (i) an infall of metal-poor and relatively
low-[$\alpha$/Fe] gas, and (ii) a radial flow where already chemically-enriched
gas moves inwards with an average velocity of $\sim0.7$ km/s. Moreover, we find
that stellar migrations mostly happen outwards, on typical time scales of
$\sim5$ Gyr. Our predicted radial metallicity gradients agree with the
observations from APOGEE-DR16, and the main effect of stellar migrations is to
flatten the radial metallicity profiles by 0.05 dex/kpc in the slopes. We also
show that the effect of migrations can appear more important in [$\alpha$/Fe]
than in the [Fe/H]-age relation of thin-disc stars.
