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El-Badry K, Bland-Hawthorn J, Wetzel A, Quataert E, Weisz DR, Boylan-Kolchin M, Hopkins PF, Faucher-Giguère CA, Kereš D, Garrison-Kimmel S. Where are the most ancient stars in the Milky Way? Mon Not R Astron Soc 2018; 480:652-668. [PMID: 30581239 PMCID: PMC6301095 DOI: 10.1093/mnras/sty1864] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The oldest stars in the Milky Way (MW) bear imprints of the Galaxy's early assembly history. We use FIRE cosmological zoom-in simulations of three MW-mass disc galaxies to study the spatial distribution, chemistry, and kinematics of the oldest surviving stars (z form ≳ 5) in MW-like galaxies. We predict the oldest stars to be less centrally concentrated at z = 0 than stars formed at later times as a result of two processes. First, the majority of the oldest stars are not formed in situ but are accreted during hierarchical assembly. These ex situ stars are deposited on dispersion-supported, halo-like orbits but dominate over old stars formed in situ in the solar neighbourhood, and in some simulations, even in the galactic centre. Secondly, old stars formed in situ are driven outwards by bursty star formation and energetic feedback processes that create a time-varying gravitational potential at z ≳ 2, similar to the process that creates dark matter cores and expands stellar orbits in bursty dwarf galaxies. The total fraction of stars that are ancient is more than an order of magnitude higher for sight lines away from the bulge and inner halo than for inward-looking sight lines. Although the task of identifying specific stars as ancient remains challenging, we anticipate that million-star spectral surveys and photometric surveys targeting metal-poor stars already include hundreds of stars formed before z = 5. We predict most of these targets to have higher metallicity (-3 < [Fe/H] < -2) than the most extreme metal-poor stars.
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Affiliation(s)
- Kareem El-Badry
- Department of Astronomy and Theoretical Astrophysics Center, University of California Berkeley, Berkeley, CA 94720, USA
| | - Joss Bland-Hawthorn
- Miller Institute, University of California Berkeley, Berkeley, CA 94720, USA
- Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO-3D), Sydney, NSW 2006, Australia
- Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006, Australia
| | - Andrew Wetzel
- Department of Physics, University of California, Davis, CA 95616, USA
| | - Eliot Quataert
- Department of Astronomy and Theoretical Astrophysics Center, University of California Berkeley, Berkeley, CA 94720, USA
| | - Daniel R. Weisz
- Department of Astronomy and Theoretical Astrophysics Center, University of California Berkeley, Berkeley, CA 94720, USA
| | | | - Philip F. Hopkins
- TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125, USA
| | | | - Dušan Kereš
- Department of Physics, Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093, USA
| | - Shea Garrison-Kimmel
- TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125, USA
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