Evidence from APOGEE for the presence of a major building block of the halo buried in the inner Galaxy

Abstract

We report evidence from APOGEE for the presence of a new metal-poor stellar structure located within $\sim$4~kpc of the Galactic centre. Characterised by a chemical composition resembling those of low mass satellites of the Milky Way, this new inner Galaxy structure (IGS) seems to be chemically and dynamically detached from more metal-rich populations in the inner Galaxy. We conjecture that this structure is associated with an accretion event that likely occurred in the early life of the Milky Way. Comparing the mean elemental abundances of this structure with predictions from cosmological numerical simulations, we estimate that the progenitor system had a stellar mass of $\sim 5\times 10^8{M}_{\odot }$, or approximately twice the mass of the recently discovered Gaia-Enceladus/Sausage system. We find that the accreted:{\it in situ} ratio within our metal-poor ([Fe/H]$<$--0.8) bulge sample is somewhere between 1:3 and 1:2, confirming predictions of cosmological numerical simulations by various groups.

Accepted for publication in MNRAS. 22 pages, 13 Figures

References in corpus (47)

• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• The 2.5 m Telescope of the Sloan Digital Sky Survey
• galpy: A Python Library for Galactic Dynamics
• The EAGLE simulations of galaxy formation: calibration of subgrid physics and model variations
• The mass distribution and gravitational potential of the Milky Way
• 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
• Streams, substructures and the early history of the Milky Way
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE) Spectrographs
• Target Selection for the SDSS-IV APOGEE-2 Survey
• Kraken reveals itself -- the merger history of the Milky Way reconstructed with the E-MOSAICS simulations
• The GALAH Survey: Observational Overview and Gaia DR1 companion
• Tracing chemical evolution over the extent of the Milky Way's Disk with APOGEE Red Clump Stars
• The age-metallicity structure of the Milky Way disk
• Reverse engineering the Milky Way
• Disentangling the Galactic Halo with APOGEE: I. Chemical and Kinematical Investigation of Distinct Metal-Poor Populations
• The Gaia-ESO Survey: metallicity and kinematic trends in the Milky Way bulge
• The total stellar halo mass of the Milky Way
• The E-MOSAICS project: tracing galaxy formation and assembly with the age-metallicity distribution of globular clusters
• The Bulge Radial Velocity Assay (BRAVA): I. Sample Selection and a Rotation Curve
• Weighing the stellar constituents of the Galactic halo with APOGEE red giant stars
• The Chemical Compositions of Accreted and {\it in situ} Galactic Globular Clusters According to SDSS/APOGEE
• A relationship between specific star formation rate and metallicity gradient within z=1 galaxies from KMOS-HiZELS
• SDSS-IV MaNGA: stellar population gradients as a function of galaxy environment
• The Pristine Inner Galaxy Survey (PIGS) I: Tracing the kinematics of metal-poor stars in the Galactic bulge
• The first all-sky view of the Milky Way stellar halo with Gaia+2MASS RR Lyrae
• How Many Components? Quantifying the Complexity of the Metallicity Distribution in the Milky Way Bulge with APOGEE
• Metallicity and $\alpha$-element Abundance Gradients along the Sagittarius Stream as Seen by APOGEE
• The age of the Milky Way inner stellar spheroid from RR Lyrae population synthesis
• The Bulge Radial Velocity Assay for RR Lyrae stars (BRAVA-RR) DR2: a Bimodal Bulge?
• The Pristine Inner Galaxy Survey (PIGS) II: Uncovering the most metal-poor populations in the inner Milky Way
• The origin of stellar populations in the Galactic bulge from chemical abundances
• The contribution of N-rich stars to the Galactic stellar halo using APOGEE red giants
• The bimodal [Mg/Fe] versus [Fe/H] bulge sequence as revealed by APOGEE DR14
• Exploring the stellar age distribution of the Milky Way Bulge using APOGEE
• Purveyors of fine halos: Re-assessing globular cluster contributions to the Milky Way halo build-up with SDSS-IV
• The Bulge Metallicity Distribution from the APOGEE Survey
• Predicting accreted satellite galaxy masses and accretion redshifts based on globular cluster orbits in the E-MOSAICS simulations
• Baade's window with APOGEE: Metallicities, ages and chemical abundances
• Kinematics in the Galactic Bulge with APOGEE: II. High-Order Kinematical Moments and Comparison to Extragalactic Bar Diagnostics
• Purveyors of fine halos. II. Chemodynamical association of halo stars with Milky Way globular clusters
• Was the Milky Way Bulge Formed From The Buckling Disk Instability, Hierarchical Collapse, Accretion of Clumps, or All of the Above?
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• Constraints on the Galactic Inner Halo Assembly History from the Age Gradient of Blue Horizontal-branch Stars
• Gaia DR2 orbital properties for field stars with globular cluster-like CN band strengths
• The building blocks of the Milky Way halo using APOGEE and Gaia -- or -- Is the Galaxy a typical galaxy?

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