A detailed reconstruction of the early Milky Way from its most metal-poor stars

The Gaia mission is providing many details on the dynamical complexity of our Galaxy, now and in the past. However, the picture of the Milky Way history becomes very incomplete at early times. The scarcity of well-studied early generations stars throughout different environments, represented by the lowest metallicity stars, limits us severely to study the era of First Stars and early Galaxy assembly. Next generation massively multiplexed instruments will soon complement Gaia astrometry to its faint limit with crucial radial velocities and chemical abundance patterns. Specifically, the Northern WEAVE and Southern 4MOST surveys will finally provide the high-priority targeting of the most metal-poor stars in low- and high-resolution needed.The aim of this EARLYMW ERC is to use these surveys to move the known history of our Galaxy back much farther to the first billion years after the Big Bang. I am in a unique position to make this step up from analysis of scarce individual stars to population studies, as I am leading the relevant very metal-poor target selection and survey efforts. To achieve the aim, my team and I will, after careful correction for selection effects (i) compare the chemical enrichment of early generations across Galactic components, and (ii) follow up very metal-poor tails of dynamical substructures and assess their dependence on progenitor properties. We will then compare our findings with cosmological simulations varying assumptions on early chemical enrichment.This EARLYMW project will, for the first time, provide a complete census of very metal-poor stars across various Milky Way components and quantitatively assess early enrichment processes as function of environment. Our results will constrain physical parameters for early Universe enrichment and map contributions of early supernovae explosions at much smaller scales than possible at high redshift. EARLYMW will deliver a quantitative picture of the proto-galaxy that became our Milky Way.