Selecting accreted populations: metallicity, elemental abundances, and ages of the Gaia-Sausage-Enceladus and Sequoia populations

Abstract

Identifying stars found in the Milky Way as having formed in situ or accreted can be a complex and uncertain undertaking. We use Gaia kinematics and APOGEE elemental abundances to select stars belonging to the Gaia-Sausage-Enceladus (GSE) and Sequoia accretion events. These samples are used to characterize the GSE and Sequoia population metallicity distribution functions, elemental abundance patterns, age distributions, and progenitor masses. We find that the GSE population has a mean [Fe/H] $\sim -1.15$ and a mean age of $10-12$ Gyr. GSE has a single sequence in [Mg/Fe] vs [Fe/H] consistent with the onset of SN Ia Fe contributions and uniformly low [Al/Fe] of $\sim -0.25$ dex. The derived properties of the Sequoia population are strongly dependent on the kinematic selection. We argue the selection with the least contamination is $J_ϕ/J_{\mbox{tot}} < -0.6$ and $(J_z - J_R)/J_{\mbox{tot}} < 0.1$. This results in a mean [Fe/H] $\sim -1.3$ and a mean age of $12-14$ Gyr. The Sequoia population has a complex elemental abundance distribution with mainly high [Mg/Fe] stars. We use the GSE [Al/Fe] vs [Mg/H] abundance distribution to inform a chemically-based selection of accreted stars, which is used to remove possible contaminant stars from the GSE and Sequoia samples.

21 pages, 15 figures, MNRAS accepted

References in corpus (34)

• galpy: A Python Library for Galactic Dynamics
• The DESI Experiment Part I: Science,Targeting, and Survey Design
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• Gaia-2MASS 3D maps of Galactic interstellar dust within 3 kpc
• 4MOST: Project overview and information for the First Call for Proposals
• The DESI Experiment Part II: Instrument Design
• Young [$\alpha$/Fe]-enhanced stars discovered by CoRoT and APOGEE: What is their origin?
• The Streams of the Gaping Abyss: A population of entangled stellar streams surrounding the Inner Galaxy
• Reverse engineering the Milky Way
• Reconstructing the Last Major Merger of the Milky Way with the H3 Survey
• Distances and parallax bias in Gaia DR2
• Disentangling the Galactic Halo with APOGEE: I. Chemical and Kinematical Investigation of Distinct Metal-Poor Populations
• Non-LTE aluminium abundances in late-type stars
• The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage
• Timing the Early Assembly of the Milky Way with the H3 Survey
• SDSS-V: Pioneering Panoptic Spectroscopy
• Weighing the stellar constituents of the Galactic halo with APOGEE red giant stars
• Origin of the excess of high-energy retrograde stars in the Galactic halo
• APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy
• Elevated r-process enrichment in Gaia Sausage and Sequoia
• No evidence of chemical anomalies in the bimodal turnoff cluster NGC 1806 in the LMC
• Disentangling the Galactic Halo with APOGEE: II. Chemical and Star Formation Histories for the Two Distinct Populations
• Preliminary Target Selection for the DESI Milky Way Survey (MWS)
• The origin of the spurious iron spread in the globular cluster NGC 3201
• The tale of the tail -- disentangling the high transverse velocity stars in Gaia DR2
• Identifying Sagittarius Stream Stars By Their APOGEE Chemical Abundance Signatures
• Tagging the Chemical Evolution History of the Large Magellanic Cloud Disk
• A chemo-dynamical link between the Gjöll stream and NGC 3201
• The tidal stream generated by the globular cluster NGC 3201
• Connecting the local stellar halo and its dark matter density to dwarf galaxies via blue stragglers
• Estimating the age-metallicity distribution of a stellar sample from the probability distributions of the individual stars
• Modelling the chemical evolution of the Milky Way

Cited by in corpus (67)

• The Global Dynamical Atlas of the Milky Way mergers: Constraints from Gaia EDR3 based orbits of globular clusters, stellar streams and satellite galaxies
• The chemical characterisation of halo substructure in the Milky Way based on APOGEE
• The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and $Gaia$ eDR3
• Galactic Archaeology with Gaia
• GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos
• Gaia Data Release 3: Chemical cartography of the Milky Way
• Stellar halo substructure generated by bar resonances
• Substructure in the stellar halo near the Sun. I. Data-driven clustering in Integrals of Motion space
• Energy wrinkles and phase-space folds of the last major merger
• High-precision chemical abundances of Galactic building blocks. The distinct chemical abundance sequence of Sequoia
• The detailed chemical abundance patterns of accreted halo stars from the optical to infrared
• A Comparative Analysis of the Chemical Compositions of Gaia-Enceladus/Sausage and Milky Way Satellites using APOGEE
• Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) I. The final word on the origin of NGC6388 and NGC6441
• Radial halo substructure in harmony with the Galactic bar
• DESI Early Data Release Milky Way Survey Value-Added Catalogue
• VINTERGATAN-GM: The cosmological imprints of early mergers on Milky-Way-mass galaxies
• Metallicity distributions of halo stars: do they trace the Galactic accretion history?
• The stellar parameters and elemental abundances from low-resolution spectra I: 1.2 million giants from LAMOST DR8
• The stellar halo in Local Group Hestia simulations II. The accreted component
• The stellar halo in Local Group Hestia simulations III. Chemical abundance relations for accreted and in-situ stars
• Chronology of the chemical enrichment of the old Galactic stellar populations
• The Galactic Distribution of Phosphorus: A Survey of 163 Disk and Halo Stars
• The cerium content of the Milky Way as revealed by Gaia DR3 GSP-Spec abundances
• MINCE I. Presentation of the project and of the first year sample
• Classifying globular clusters and applying them to estimate the mass of the Milky Way
• An old, metal-rich accreted stellar component in the Milky Way stellar disk
• Gaia-Sausage-Enceladus star formation history as revealed by detailed elemental abundances
• Dynamics of Stellar Disk Tilting from Satellite Mergers
• Galactic ArchaeoLogIcaL ExcavatiOns (GALILEO) II. t-SNE Portrait of Local Fossil Relics and Structures
• Gaia-IGRINS synergy: Orbits of Newly Identified Milky Way Star Clusters
• Exploring the chemodynamics of metal-poor stellar populations
• High-speed stars. II. An unbound star, young stars, bulge metal-poor stars, and Aurora candidates
• Characterisation of local halo building blocks: Thamnos and Sequoia
• Influence of the Gaia-Sausage-Enceladus on the density shape of the Galactic stellar halo revealed by halo K giants from the LAMOST survey
• New stellar velocity substructures from Gaia DR3 proper motions
• The in situ origin of the globular cluster NGC 6388 from abundances of Sc, V, and Zn of a large sample of stars
• Evidence of Gaia Enceladus experiencing at least two passages around the Milky Way
• Peeking beneath the precision floor -- II. Probing the chemo-dynamical histories of the potential globular cluster siblings, NGC 288 and NGC 362
• Beryllium abundances in turn-off stars of globular clusters with the CUBES spectrograph
• Dynamical streams in the local stellar halo
• Chronology of our Galaxy from Gaia colour-magnitude diagram fitting (ChronoGal) -- III. Age and metallicity distribution of Gaia-Sausage-Enceladus stars near the Sun
• Cosmological Simulations of Stellar Halos with Gaia Sausage-Enceladus Analogues: Two Sausages, One Bun?
• MINCE III. Detailed chemical analysis of the UVES sample
• Magnesium isotope ratios in Milky Way and dwarf galaxy stars
• Revealing the Milky Way's Most Recent Major Merger with a Gaia EDR3 Catalog of Machine-Learned Line-of-Sight Velocities
• Unveiling the nature of HE 0107-5240
• A New Tidal Stream Discovered in Gaia DR3
• The dawn is quiet here: Rise in [$\alpha$/Fe] is a signature of massive gas accretion that fueled proto-Milky Way
• On the Use of Field RR Lyrae as Galactic Probes -- VIII. Early Formation of the Galactic Spheroid
• Disentanglement of the chemodynamical assembly: mapping the Milky Way disks
• Rediscovering the Milky Way with orbit superposition approach and APOGEE data III. Panoramic view of the bulge
• The Spheroidal Bulge of the Milky Way: Chemodynamically Distinct from the Inner-Thick Disc and Bar
• Build-up and survival of the disc: From numerical models of galaxy formation to the Milky Way
• Unveiling Galactic substructures with M Giant stars: A kinematic and chemical study based on LAMOST DR9, Gaia DR3 and APOGEE DR17
• The metal-poorest tail of the Galactic halo: hypothesis on its origin from precise spectral analysis
• The accreted Galaxy: An overview of TESS metal-poor accreted stars candidates
• Searching for stars ejected from the Galactic Centre in DESI
• Disentangling Milky Way halo populations at low metallicities using [Al/Fe]
• A Sequoia stellar candidate with very high 7Li and 9Be
• GSE vs. LMC: reshaping of radially biased stellar haloes by satellites
• The R-Process Alliance: A Nearly Complete R-Process Abundance Template Derived from Ultraviolet Spectroscopy of the R-Process-Enhanced Metal-Poor Star HD 222925
• The Two-infall Model Revisited: Constraints on Milky Way Bulge Assembly from >30,000 Galactic Chemical Evolution Models and Machine Learning
• The chemodynamical memory of a major merger in a NIHAO-UHD Milky Way analogue -- I. A golden thread through time and space
• Searching for and characterizing halo substructures with the GALAH DR4 survey
• Gaia-Sausage-Enceladus: Lithium evolution from early red-giant-branch and main-sequence stars
• The GALAH Survey: Neutron-Capture Elemental Abundances for 350,000 Gaia-RVS spectra and the Chemodynamics of Accreted Structures
• How to Build an Empirical Speed Distribution for Dark Matter in the Solar Neighborhood