The GALAH Survey: Accreted stars also inhabit the Spite Plateau

Abstract

The ESA Gaia astrometric mission has enabled the remarkable discovery that a large fraction of the stars near the Solar neighbourhood appear to be debris from a single in-falling system, the so-called Gaia-Enceladus-Sausage (GSE). One exciting feature of this result is that it gives astronomers for the first time a large sample of easily observable unevolved stars that formed in an extra-Galactic environment, which can be compared to stars that formed within our Milky Way. Here we use these stars to investigate the "Spite Plateau" -- the near-constant lithium abundance observed in metal-poor dwarf stars across a wide range of metallicities (-3<[Fe/H]<-1). In particular our aim is to test whether the stars that formed in the GSE show a different Spite Plateau to other Milky Way stars that inhabit the disk and halo. Individual galaxies could have different Spite Plateaus -- e.g., the ISM could be more depleted in lithium in a lower galactic mass system due to it having a smaller reservoir of gas. We identified 76 GSE dwarf stars observed and analyzed by the GALactic Archeology with HERMES (GALAH) survey as part of its Third Data Release. Orbital actions were used to select samples of Gaia-Enceladus stars, and comparison samples of halo and disk stars. We find that the Gaia-Enceladus stars show the same lithium abundance as other likely accreted stars and in situ Milky Way stars, strongly suggesting that the "lithium problem" is not a consequence of the formation environment. This result fits within the growing consensus that the Spite Plateau, and more generally the "cosmological lithium problem" -- the observed discrepancy between the amount of lithium in warm, metal-poor dwarf stars in our Galaxy, and the amount of lithium predicted to have been produced by Big Bang Nucleosynthesis -- is the result of lithium depletion processes within stars.

12 pages, 7 figures, updated version resubmitted to MNRAS after responding to positive referee report. Also now has attached galah_spite_stars.csv file which is full version of Table 1

References in corpus (30)

• The Gaia mission
• galpy: A Python Library for Galactic Dynamics
• The mass distribution and gravitational potential of the Milky Way
• The GALAH Survey: Scientific Motivation
• The GALAH+ Survey: Third Data Release
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• The Primordial Lithium Problem
• The effects of He I 10830 on helium abundance determinations
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• First stars VII. Lithium in extremely metal poor dwarfs
• The GALAH Survey: Observational Overview and Gaia DR1 companion
• The Streams of the Gaping Abyss: A population of entangled stellar streams surrounding the Inner Galaxy
• The TESS-HERMES survey Data Release 1: high-resolution spectroscopy of the TESS southern continuous viewing zone
• Disentangling the Hercules stream
• The Chemical Compositions of Accreted and {\it in situ} Galactic Globular Clusters According to SDSS/APOGEE
• A Sequoia in the Garden: FSR 1758 - Dwarf Galaxy or Giant Globular Cluster?
• The Southern Stellar Stream Spectroscopic Survey (S5): Chemical Abundances of Seven Stellar Streams
• The oldest and most metal poor stars in the APOSTLE Local Group simulations
• Fourteen candidate RR Lyrae star streams in the inner Galaxy
• The GALAH survey: The data reduction pipeline
• From First Stars to the Spite Plateau: a Possible Reconciliation of Halo Stars Observations with Predictions from Big Bang Nucleosynthesis
• Boron Abundances Across the "Li-Be Dip" in the Hyades
• Light Elements in the Universe
• The GALAH Survey: A new constraint on cosmological lithium and Galactic lithium evolution from warm dwarf stars
• Where did the globular clusters of the Milky Way form? Insights from the E-MOSAICS simulations
• The S2 Stream: the shreds of a primitive dwarf galaxy
• Lithium and Beryllium in the Gaia-Enceladus Galaxy
• The GALAH Survey: Chemically tagging the Fimbulthul stream to the globular cluster $\omega$ Centauri
• The cosmological Lithium problem outside the Galaxy: the Sagittarius globular cluster M54
• Connecting the local stellar halo and its dark matter density to dwarf galaxies via blue stragglers

Cited by in corpus (15)

• The GALAH+ Survey: Third Data Release
• Reconstructing the Last Major Merger of the Milky Way with the H3 Survey
• The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and $Gaia$ eDR3
• The Complexity of the Cetus Stream Unveiled from the Fusion of STREAMFINDER and StarGO
• The stellar halo in Local Group Hestia simulations II. The accreted component
• The Cetus-Palca stream: A disrupted small dwarf galaxy. A prequel to the science possible with WEAVE with precise spectro-photometric distances
• The metal-poor end of the Spite plateau. II. Detailed chemical investigation
• Search for Extremely Metal-Poor Stars with GEMINI-N/GRACES I. Chemical-Abundance Analysis
• The GALAH Survey: No chemical evidence of an extragalactic origin for the Nyx stream
• Lithium in the lower red giant branch of 5 Galactic globular clusters
• The role of radial migration on tracing lithium evolution in the Galactic disk
• Main-sequence Turnoff Stars as Probes of the Ancient Galactic Relic: Chemo-dynamical Analysis of a Pilot Sample
• A Sequoia stellar candidate with very high 7Li and 9Be
• Gaia-Sausage-Enceladus: Lithium evolution from early red-giant-branch and main-sequence stars
• Searching for and characterizing halo substructures with the GALAH DR4 survey