The imprint of clump formation at high redshift – I. A disc α-abundance dichotomy

The disc structure of the Milky Way is marked by a chemical dichotomy, with high-α and low-α abundance sequences, traditionally identified with the geometric thick and thin discs. This identification is aided by the old ages of the high-α stars, and lower average ages of the low-α ones. Recent large-scale surveys such as APOGEE have provided a wealth of data on this chemical structure, including s...