The Unmixed Debris of Gaia-Sausage/Enceladus in the Form of a Pair of Halo Stellar Overdensities

Abstract

In the first billion years after its formation, the Galaxy underwent several mergers with dwarf satellites of various masses. The debris of Gaia-Sausage/Enceladus (GSE), the galaxy responsible for the last significant merger of the Milky Way, dominates the inner halo and has been suggested to be the progenitor of both the Hercules-Aquila Cloud (HAC) and Virgo Overdensity (VOD). We combine SEGUE, APOGEE, Gaia, and StarHorse distances to characterize the chemodynamical properties and verify the link between HAC, VOD, and GSE. We find that the orbital eccentricity distributions of the stellar overdensities and GSE are comparable. We also find that they have similar, strongly peaked, metallicity distribution functions, reinforcing the hypothesis of common origin. Furthermore, we show that HAC and VOD are indistinguishable from the prototypical GSE population within all chemical-abundance spaces analyzed. All these evidences combined provide a clear demonstration that the GSE merger is the main progenitor of the stellar populations found within these halo overdensities.

Paper accepted for publication in ApJ Letters

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Cited by in corpus (12)

• StarHorse results for spectroscopic surveys + Gaia DR3: Chrono-chemical populations in the solar vicinity, the genuine thick disk, and young-alpha rich stars
• Galactic Archaeology with Gaia
• Distant Echoes of the Milky Way's Last Major Merger
• Mapping the anisotropic Galactic stellar halo with Blue Horizontal Branch stars
• Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ($[Fe/H]\lesssim -3$) Regime
• Exploring the diversity and similarity of radially anisotropic Milky Way-like stellar haloes: implications for disrupted dwarf galaxy searches
• Chronology of the chemical enrichment of the old Galactic stellar populations
• A determination of the LMC dark matter subhalo mass using the MW halo stars in its gravitational wake
• The Pristine Survey -- XXVII. Journey to the Galactic outskirts -- Mapping the outer halo red giant stars down to the very metal-poor end
• Discovery of the shell structure via break radii in the outer halo of the Milky Way
• The Chemodynamical Nature of the Triangulum-Andromeda Overdensity
• GSE vs. LMC: reshaping of radially biased stellar haloes by satellites