Galactic and extragalactic archaeologists have long tried to connect the dots between the Milky Way and the early Universe, often borrowing each other’s terminology. Stephanie Monty and colleagues propose using the chemical space parameterized by iron and oxygen abundances to reconstruct a comprehensive picture of the Galaxy at ‘cosmic noon’ (z ≈ 2–3).
The authors collect abundance data from GALAH DR3 for resolved stellar populations in the Galaxy and the Local Group, including high- and low-alpha disk stars, in situ and accreted halo stars, globular clusters, planetary nebulae in M31, and satellite galaxies. Separately, Fe and O abundances of star-forming galaxies at cosmic noon are taken from four galaxy surveys, with O abundances adjusted for dust depletion. All data from both Local Group and cosmic noon galaxies are scaled to a solar reference to provide a consistent view of chemical enrichment across cosmic time.