Abstract

Contributed Talk - Splinter 4MOST   (MW-0337)

First insights into Milky Way halo substructures from 4MOST HR SPV spectra

Susmitha Antony, Tadafumi Matsuno, Norbert Christlieb, Hans-Günter Ludwig, IWG7, IWG7, SPV team
ZAH/LSW, ZAH/ARI, ZAH/LSW, ZAH/LSW, 4MOST

One of the major goals of the 4MOST S2 survey is to reconstruct the Milky Way’s merger history using the chemical, kinematical, and dynamical properties of halo stars. The abundances of alpha, odd Z, and Fe-peak elements are especially important as they trace star-formation histories, chemical-enrichment timescales, and can be used to distinguish accreted stars from in-situ populations due to their systematically lower abundance patterns. This makes them a powerful diagnostic of past merger events. During the Survey Program Validation (SPV) phase, HR spectra were obtained for kinematically selected stars in known halo substructures (e.g., Gaia–Sausage–Enceladus, Helmi streams, Thamnos) and thick-disk stars. Additional targets from the regular catalogue of S2 and our supplementary target program were observed as fillers during SPV. In total, about 3000 stars have been observed so far. In my talk, I will present chemical abundances of these stars derived from the HR spectra using the 4MOST Galactic Pipeline revealing both the presence of accreted substructures in the general catalogue and distinct abundance patterns among the kinematically selected groups. We also identify new candidate members not previously associated with known substructures. These results demonstrate the capability of 4MOST to chemically characterize halo substructures and provide a preliminary estimate of the precision achievable over the 5-year survey program.