How homogeneous was the chemical enrichment of the Milky Way 13 gigayears ago?

Abstract

We reanalyze the chemical composition of the metal-poorest tail of the Galactic halo using highly accurate atmospheric parameters (Giribaldi et al. 2021, 2023) and cutting-edge 3D NLTE models (Amarsi et al. 2018). Most [Mg/Fe] versus [Fe/H] diagrams in the literature exhibit significant scatter at [Fe/H] ≲ – 2 dex, often interpreted as evidence of inhomogeneous enrichment during the early phases of galaxy evolution (e.g., Rossi et al. 2021). However, our analysis of observational data reveals that in the range –3.5< [Fe/H] <–2 dex, the [Mg/Fe] versus [Fe/H] distribution is relatively narrow. This finding suggests a low degree of stochastic enrichment in magnesium during these epochs in the Milky Way halo.