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

References in corpus (10)

• The Gaia mission
• The mass distribution and gravitational potential of the Milky Way
• Tracing Galaxy Formation with Stellar Halos II: Relating Substructure in Phase- and Abundance-Space to Accretion Histories
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• From dawn till disk: Milky Way's turbulent youth revealed by the APOGEE+Gaia data
• The Hercules-Aquila Cloud
• Timing the Early Assembly of the Milky Way with the H3 Survey
• A Low-Mass Stellar-Debris Stream Associated with a Globular Cluster Pair in the Halo
• Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys
• Identification of Sagittarius stream members in Angular Momentum space with Gaussian mixture techniques

Cited by in corpus (3)

• StarHorse results for spectroscopic surveys + Gaia DR3: Chrono-chemical populations in the solar vicinity, the genuine thick disk, and young-alpha rich stars
• Chronology of the chemical enrichment of the old Galactic stellar populations
• The Chemodynamical Nature of the Triangulum-Andromeda Overdensity