期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 501, 期 4, 页码 5981-5996出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stab003
关键词
stars: kinematics and dynamics; stars: Population II; Galaxy: bulge; Galaxy: evolution
资金
- TDA/Scialog (2018-2020) grant - Research Corporation
- TDA/Scialog grant (2019-2021) - Heising-Simons Foundation
- National Science Foundation [AST-1907417]
- Wootton Center for Astrophysical Plasma Properties under the United States Department of Energy [DE-NA0003843]
- Science and Technology Facility Council (STFC) [ST/R000786/1]
- Swedish Research Council [2018-04857]
- AustralianResearchCouncil (ARC) Future Fellowship [FT160100402]
- UK Science and Technology Facility Council (STFC) [ST/R000905/1]
- European Union [797100]
- STFC [ST/R000905/1, ST/M000958/1, ST/R000786/1] Funding Source: UKRI
- Marie Curie Actions (MSCA) [797100] Funding Source: Marie Curie Actions (MSCA)
Through spectroscopic and orbital analysis, we have gained insights into the origins and properties of metal-poor stars in the bulge of the Milky Way, identifying at least two distinct populations within this region.
The metal-poor stars in the bulge are important relics of the Milky Way's formation history, as simulations predict that they are some of the oldest stars in the Galaxy. In order to determine if they are truly ancient stars, we must understand their origins. Currently, it is unclear if the metal-poor stars in the bulge ([Fe/H] < -1 dex) are merely halo interlopers, a unique accreted population, part of the boxy/peanut-shaped bulge, or a classical bulge population. In this work, we use spectra from the VLT/FLAMES spectrograph to obtain metallicity estimates using the Ca-II triplet of 473 bulge stars (187 of which have [Fe/H] < -1 dex), targeted using SkyMapper photometry. We also use Gaia DR2 data to infer the Galactic positions and velocities along with orbital properties for 523 stars. We employ a probabilistic orbit analysis and find that about half of our sample has a >50 per cent probability of being bound to the bulge, and half are halo interlopers. We also see that the occurrence rate of halo interlopers increases steadily with decreasingmetallicity across the full range of our sample (-3<[Fe/H]< 0.5). Our examination of the kinematics of the confined compared to the unbound stars indicates themetal-poor bulge comprises at least two populations; those confined to the boxy/peanut bulge and halo stars passing through the inner galaxy. We conclude that an orbital analysis approach, as we have employed, is important to understand the composite nature of the metal-poor stars in the inner region.
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