Formation of Galactic Disks I: Why Did the Milky Way's Disk Form Unusually Early?

Understand

Recent results from spectroscopic and astrometric surveys of nearby stars suggest that the stellar disk of our Milky Way (MW) was formed quite early, within the first few billion years of its evolution.

• Chemokinematic signatures of disk formation in cosmological zoom-in simulations appear to be in tension with these data, implying that MW-like disk formation is delayed in simulations.
• We investigate the formation of galactic disks using a representative sample of MW-like galaxies from the cosmological-volume simulation TNG50.
• We find that on average MW-mass disks indeed form later than the local data suggest.