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

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.

5 pages, 5 figures, Accepted 2023 March 6 in MNRAS

References in corpus (16)

• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• The GALAH+ Survey: Third Data Release
• The Auriga Project: the properties and formation mechanisms of disc galaxies across cosmic time
• The Biggest Splash
• A time-resolved picture of our Milky Way's early formation history
• Age dissection of the Milky Way discs: red giants in the Kepler field
• The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage
• Origin of chemically distinct discs in the Auriga cosmological simulations
• Chronologically dating the early assembly of the Milky Way
• Sausage & Mash: The dual origin of the Galactic thick disc and halo from the gas-rich Gaia-Enceladus-Sausage merger
• Weighing the stellar constituents of the Galactic halo with APOGEE red giant stars
• Two Disk Components from a Gas Rich Disk-Disk Merger
• Unveiling the Distinct Formation Pathways of the Inner and Outer Discs of the Milky Way with Bayesian Machine Learning
• Characterizing epochs of star formation across the Milky Way disc using age-metallicity distributions of GALAH stars
• Radialization of satellite orbits in galaxy mergers
• Metallicity Gradient of the Thick Disc Progenitor at High Redshift

Cited by in corpus (19)

• Galactic Archaeology with Gaia
• Spectroscopic age estimates for APOGEE red-giant stars: Precise spatial and kinematic trends with age in the Galactic disc
• Unveiling the time evolution of chemical abundances across the Milky Way disk with APOGEE
• On the origin of the Galactic thin and thick discs, their abundance gradients and the diagnostic potential of their abundance ratios
• The impact of early massive mergers on the chemical evolution of Milky Way-like galaxies: insights from NIHAO-UHD simulations
• Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) I. The final word on the origin of NGC6388 and NGC6441
• The stellar halo in Local Group Hestia simulations I. The in-situ component and the effect of mergers
• Stellar populations and origin of thick disks in AURIGA simulations
• Multi-TeV dark matter density in the inner Milky Way halo: spectral and dynamical constraints
• Galaxy archaeology for wet mergers: Globular cluster age distributions in the Milky Way and nearby galaxies
• A Blueprint for the Milky Way's Stellar Populations. IV. A String of Pearls $-$ the Galactic Starburst Sequence
• Rediscovering the Milky Way with orbit superposition approach and APOGEE data II. Chrono-chemo-kinematics of the disc
• Gamma rays from dark matter spikes in EAGLE simulations
• The effect of environment on the mass assembly history of the Milky Way and M31
• The Milky Way in context: The formation of galactic discs and chemical sequences from a cosmological perspective
• Build-up and survival of the disc: From numerical models of galaxy formation to the Milky Way
• Milky Way Mapper decoded abundances -- I. Shared disc enrichment patterns
• Dissecting stellar populations with manifold learning I. Validation of the method on a synthetic Milky Way-like galaxy
• Deciphering the Milky Way's star formation at cosmic noon with high proper-motion stars: A precursor to the merger-driven starburst