Evidence of Gaia Enceladus experiencing at least two passages around the Milky Way
arXiv:2506.00409 · doi:10.3847/2041-8213/addc66
Abstract
One of the major recent breakthroughs has been the discovery of the last Major Merger to happen in the history of the Milky Way. Around 10 Gyr ago the galaxy Gaia Enceladus, with estimated ~10% of the Milky Way mass, fell into its potential, bringing a large amount of stars which can be identified through their unique chemical and kinematic signatures. Simulations have long predicted that a galaxy of this size should experience several passages through the disk of the Milky Way before eventually being fully dispersed. For the first time, we present observational evidence to support this. We identify two subpopulations accreted from Gaia Enceladus: 1) stars which today have large kinematic energy, which originate from the outskirts of Gaia Enceladus and were accreted during early passages; 2) stars with low kinetic energy accreted at later passages, originating from the inner parts of Gaia Enceladus. Through the use of high-precision chemical abundances, crucially including new aluminum measurements, we show that in all observed abundance ratios ([Fe/H], [Al/Fe], [Mg/Fe] and [Mg/Ba]), stars with high energy show evidence of coming from a less chemically evolved outer region of Gaia Enceladus, compared to the stars with low energy. We therefore conclude that Gaia Enceladus experienced several passages before merging with the main body of our Galaxy. This discovery has wide implications for our understanding of this event, and consolidates Gaia Enceladus as a benchmark for studying galaxy mergers and hierarchical galaxy formation in extraordinary details.
arXiv commentAccepted in ApJL
References in corpus (44)
- The Gaia mission
- Gaia Data Release 3: Summary of the content and survey properties
- A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
- The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
- galpy: A Python Library for Galactic Dynamics
- The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
- Star Formation Histories, Abundances and Kinematics of Dwarf Galaxies in the Local Group
- Co-formation of the Galactic disc and the stellar halo
- Automated data reduction workflows for astronomy
- The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
- Chemical Cartography with APOGEE: Metallicity Distribution Functions and the Chemical Structure of the Milky Way Disk
- Two distinct halo populations in the solar neighborhood. Evidence from stellar abundance ratios and kinematics
- The age structure of stellar populations in the solar vicinity. Clues of a two-phase formation history of the Milky Way disk
- A direct dynamical measurement of the Milky Way's disk surface density profile, disk scale length, and dark matter profile at 4 kpc < R < 9 kpc
- In disguise or out of reach: first clues about in-situ and accreted stars in the stellar halo of the Milky Way from Gaia DR2
- The Disruption of the Sagittarius Dwarf Galaxy.
- Actions for axisymmetric potentials
- Multiple retrograde substructures in the Galactic halo: A shattered view of Galactic history
- Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy
- Using chemical tagging to redefine the interface of the Galactic disk and halo
- Two distinct halo populations in the solar neighborhood. II. Evidence from stellar abundances of Mn, Cu, Zn, Y, and Ba
- Charting the Galactic acceleration field I. A search for stellar streams with Gaia DR2 and EDR3 with follow-up from ESPaDOnS and UVES
- Ages and kinematics of chemically selected, accreted Milky Way halo stars
- Non-LTE aluminium abundances in late-type stars
- VLT/FLAMES high-resolution chemical abundances in Sculptor: a textbook dwarf spheroidal galaxy
- The SkyMapper-Gaia RVS view of the Gaia-Enceladus-Sausage -- an investigation of the metallicity and mass of the Milky Way's last major merger
- On the kinematic detection of accreted streams in the Gaia era: a cautionary tale
- Selecting accreted populations: metallicity, elemental abundances, and ages of the Gaia-Sausage-Enceladus and Sequoia populations
- New Radial Abundance Gradients for NGC 628 and NGC 2403
- GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos
- Evidence for Sub-Chandrasekhar Type Ia Supernovae from Stellar Abundances in Dwarf Galaxies
- The disc origin of the Milky Way bulge
- Non-LTE Radiative Transfer with Turbospectrum
- Near-infrared narrow-band photometry of M-giant and Mira stars: models meet observations
- Evidence for Gyr timescales of neutron star mergers from Galactic archaeology
- Energy wrinkles and phase-space folds of the last major merger
- The distribution of globular clusters in kinematic spaces does not trace the accretion history of the host galaxy
- Observational constraints on the origin of the elements. VII. NLTE analysis of Y II lines in spectra of cool stars and implications for Y as a Galactic chemical clock
- Neutron-capture elements in dwarf galaxies II: Challenges for the s- and i-processes at low metallicity
- Metallicity distributions of halo stars: do they trace the Galactic accretion history?
- The stellar halo in Local Group Hestia simulations II. The accreted component
- A 3D view of dwarf galaxies with Gaia and VLT/FLAMES I. The Sculptor dwarf spheroidal
- Gaia-Sausage-Enceladus star formation history as revealed by detailed elemental abundances
- A distinct halo population revealed from 3D non-LTE magnesium abundances
Cited by in corpus (7)
- From order to chaos: the blurred out metallicity gradient of the Gaia-Enceladus/Sausage progenitor
- Two faces of Gaia-Sausage-Enceladus: Mining the chemical abundance space with graph attention networks
- Disentangling Milky Way halo populations at low metallicities using [Al/Fe]
- The chemodynamical memory of a major merger in a NIHAO-UHD Milky Way analogue -- I. A golden thread through time and space
- The dynamical memory of tidal stellar streams: Joint inference of the Galactic potential and the progenitor of GD-1 with flow matching
- Probing the Milky Way Halo with RR Lyrae Stars from Gaia Data Release 3
- The GALAH Survey: Neutron-Capture Elemental Abundances for 350,000 Gaia-RVS spectra and the Chemodynamics of Accreted Structures