期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 482, 期 3, 页码 3426-3442出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/sty2955
关键词
Galaxy: abundances; Galaxy: formation; Galaxy: halo; Galaxy: kinematics and dynamics; Galaxy: stellar content
资金
- STFC
- European Research Council [ERC-CoG-646928-Multi-Pop]
- NSF Graduate Research Fellowship [DGE-1315231]
- Natural Sciences and Engineering Research Council of Canada (NSERC) [RGPIN-2015-05235]
- Alfred P. Sloan Fellowship
- Spanish Government [AYA2017-86389-P]
- Fondecyt-Conicyt Regular [1150334]
- Royal Society
- LJMU's Faculty of Engineering and Technology
- Alfred P. Sloan Foundation
- U.S. Department of Energy Office of Science
- Center for High-Performance Computing at the University of Utah
- Brazilian Participation Group
- Carnegie Institution for Science
- Carnegie Mellon University
- Chilean Participation Group
- French Participation Group
- Harvard-Smithsonian Center for Astrophysics
- Instituto de Astrofisica de Canarias
- Johns Hopkins University
- Kavli Institute for the Physics and Mathematics of the Universe (IPMU) / University of Tokyo
- Korean Participation Group
- Lawrence Berkeley National Laboratory
- Leibniz Institut fur Astrophysik Potsdam (AIP)
- Max-Planck-Institut fur Astronomie (MPIA Heidelberg)
- Max-Planck-Institut fur Astrophysik (MPA Garching)
- Max-Planck-Institut fur Extraterrestrische Physik (MPE)
- National Astronomical Observatories of China
- New Mexico State University
- New York University
- University of Notre Dame
- Observatario Nacional/MCTI
- Ohio State University
- Pennsylvania State University
- Shanghai Astronomical Observatory
- United Kingdom Participation Group
- Universidad Nacional Autonoma de Mexico
- University of Arizona
- University of Colorado Boulder
- University of Oxford
- University of Portsmouth
- University of Utah
- University of Virginia
- University of Washington
- University of Wisconsin
- Vanderbilt University
- Yale University
- STFC [1691072] Funding Source: UKRI
- Division Of Astronomical Sciences [1413269] Funding Source: National Science Foundation
Recent work indicates that the nearby Galactic halo is dominated by the debris from a major accretion event. We confirm that result from an analysis of APOGEE-DR14 element abundances and Gaia-DR2 kinematics of halo stars. We show that similar to 2/3 of nearby halo stars have high orbital eccentricities (e greater than or similar to 0.8), and abundance patterns typical of massive Milky Way dwarf galaxy satellites today, characterized by relatively low [Fe/H], [Mg/Fe], [Al/Fe], and [Ni/Fe]. The trend followed by high-e stars in the [Mg/Fe]-[Fe/H] plane shows a change of slope at [Fe/H]similar to -1.3, which is also typical of stellar populations from relatively massive dwarf galaxies. Low-e stars exhibit no such change of slope within the observed [Fe/H] range and show slightly higher abundances of Mg, Al, and Ni. Unlike their low-e counterparts, high-e stars show slightly retrograde motion, make higher vertical excursions, and reach larger apocentre radii. By comparing the position in [Mg/Fe]-[Fe/H] space of high-e stars with those of accreted galaxies from the EAGLE suite of cosmological simulations, we constrain the mass of the accreted satellite to be in the range 10(8.5)less than or similar to M-* less than or similar to 10(9) M-circle dot. We show that the median orbital eccentricities of debris are largely unchanged since merger time, implying that this accretion event likely happened at z less than or similar to 1.5. The exact nature of the low-e population is unclear, but we hypothesize that it is a combination of in situ star formation, high- vertical bar z disc stars, lower mass accretion events, and contamination by the low-e tail of the high-e population. Finally, our results imply that the accretion history of the Milky Way was quite unusual.
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