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

Author:

Horta Danny1ORCID,Schiavon Ricardo P1,Mackereth J Ted234ORCID,Pfeffer Joel1ORCID,Mason Andrew C1,Kisku Shobhit1,Fragkoudi Francesca5,Allende Prieto Carlos67,Cunha Katia89,Hasselquist Sten10,Holtzman Jon11,Majewski Steven R12,Nataf David13ORCID,O’Connell Robert W12,Schultheis Mathias14,Smith Verne V15

Affiliation:

1. Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK

2. School of Astronomy and Astrophysics, University of Birmingham, Edgbaston, Birmimgham B15 2TT, UK

3. Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St George Street, Toronto, ON M5S 3H8, Canada

4. Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St George Street, Toronto, ON M5S 3H4, Canada

5. Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching, Germany

6. Instituto de Astrofísica de Canarias, E-38200 La Laguna,Tenerife, Spain

7. Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain

8. University of Arizona, Tucson, AZ 85719, USA

9. Observatório Nacional, São Cristóvão, Rio de Janeiro, Brazil

10. Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA

11. New Mexico State University, Las Cruces, NM 88003, USA

12. Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325, USA

13. Center for Astrophysical Sciences and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA

14. Université Côte d’Azur, Observatoire de la Côte d’Azur, Laboratoire Lagrange, CNRS, Blvd de l’Observatoire, F-06304 Nice, France

15. National Optical Astronomy Observatories, Tucson, AZ 85719, USA

Abstract

ABSTRACT We report evidence from APOGEE for the presence of a new metal-poor stellar structure located within ∼4 kpc of the Galactic Centre. Characterized 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 ∼5 × 108 M⊙, or approximately twice the mass of the recently discovered Gaia-Enceladus/Sausage system. We find that the accreted: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.

Funder

H2020 European Research Council

University of Toronto

National Aeronautics and Space Administration

National Science Foundation

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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