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 universal ( 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 \sim 0.7 km/s .
Moreover , we find that stellar migrations mostly happen outwards , on typical time scales of \sim 5 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 .