Chasing the impact of the Gaia-Sausage-Enceladus merger on the formation of the Milky Way thick disc

Ciucă, Ioana; Kawata, Daisuke; Ting, Yuan-Sen; Grand, Robert J J; Miglio, Andrea; Hayden, Michael; Baba, Junichi; Fragkoudi, Francesca; Monty, Stephanie; Buder, Sven; Freeman, Ken

Abstract

We employ our Bayesian Machine Learning framework BINGO (Bayesian INference for Galactic archaeOlogy) to obtain high-quality stellar age estimates for 68 360 red giant and red clump stars present in the 17th data release of the Sloan Digital Sky Survey, the APOGEE-2 high-resolution spectroscopic survey. By examining the denoised age-metallicity relationship of the Galactic disc stars, we identify a drop in metallicity with an increase in [Mg/Fe] at an early epoch, followed by a chemical enrichment episode with increasing [Fe/H] and decreasing [Mg/Fe]. This result is congruent with the chemical evolution induced by an early-epoch gas-rich merger identified in the Milky Way-like zoom-in cosmological simulation Auriga. In the initial phase of the merger of Auriga 18 there is a drop in metallicity due to the merger diluting the metal content and an increase in the [Mg/Fe] of the primary galaxy. Our findings suggest that the last massive merger of our Galaxy, the Gaia-Sausage-Enceladus, was likely a significant gas-rich merger and induced a starburst, contributing to the chemical enrichment and building of the metal-rich part of the thick disc at an early epoch.

Citation

Ciucă, I., Kawata, D., Ting, Y., Grand, R. J. J., Miglio, A., Hayden, M., …Freeman, K. (2024). Chasing the impact of the Gaia-Sausage-Enceladus merger on the formation of the Milky Way thick disc. Monthly Notices of the Royal Astronomical Society: Letters, 528(1), L122–L126. https://doi.org/10.1093/mnrasl/slad033

• Journal Article Type: Article
• Acceptance Date: Mar 6, 2023
• Online Publication Date: Mar 11, 2023
• Publication Date: 2024-02
• Deposit Date: Feb 6, 2024
• Publicly Available Date: Feb 6, 2024
• Journal: Monthly Notices of the Royal Astronomical Society: Letters
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 528
• Issue: 1
• Pages: L122–L126
• DOI: https://doi.org/10.1093/mnrasl/slad033
• Public URL: https://durham-repository.worktribe.com/output/2227791