The COMBS Survey - II. Distinguishing the metal-poor bulge from the halo interlopers

Research output: Contribution to journalReview article

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The COMBS Survey - II. Distinguishing the metal-poor bulge from the halo interlopers. / Lucey, Madeline; Hawkins, Keith; Ness, Melissa; Debattista, Victor P.; Luna, Alice; Asplund, Martin; Bensby, Thomas; Casagrande, Luca; Feltzing, Sofia; Freeman, Kenneth C.; Kobayashi, Chiaki; Marino, Anna F.

In: Monthly Notices of the Royal Astronomical Society, Vol. 501, No. 4, 2021, p. 5981-5996.

Research output: Contribution to journalReview article

Harvard

Lucey, M, Hawkins, K, Ness, M, Debattista, VP, Luna, A, Asplund, M, Bensby, T, Casagrande, L, Feltzing, S, Freeman, KC, Kobayashi, C & Marino, AF 2021, 'The COMBS Survey - II. Distinguishing the metal-poor bulge from the halo interlopers', Monthly Notices of the Royal Astronomical Society, vol. 501, no. 4, pp. 5981-5996. https://doi.org/10.1093/mnras/stab003

APA

Lucey, M., Hawkins, K., Ness, M., Debattista, V. P., Luna, A., Asplund, M., Bensby, T., Casagrande, L., Feltzing, S., Freeman, K. C., Kobayashi, C., & Marino, A. F. (2021). The COMBS Survey - II. Distinguishing the metal-poor bulge from the halo interlopers. Monthly Notices of the Royal Astronomical Society, 501(4), 5981-5996. https://doi.org/10.1093/mnras/stab003

CBE

Lucey M, Hawkins K, Ness M, Debattista VP, Luna A, Asplund M, Bensby T, Casagrande L, Feltzing S, Freeman KC, Kobayashi C, Marino AF. 2021. The COMBS Survey - II. Distinguishing the metal-poor bulge from the halo interlopers. Monthly Notices of the Royal Astronomical Society. 501(4):5981-5996. https://doi.org/10.1093/mnras/stab003

MLA

Vancouver

Author

Lucey, Madeline ; Hawkins, Keith ; Ness, Melissa ; Debattista, Victor P. ; Luna, Alice ; Asplund, Martin ; Bensby, Thomas ; Casagrande, Luca ; Feltzing, Sofia ; Freeman, Kenneth C. ; Kobayashi, Chiaki ; Marino, Anna F. / The COMBS Survey - II. Distinguishing the metal-poor bulge from the halo interlopers. In: Monthly Notices of the Royal Astronomical Society. 2021 ; Vol. 501, No. 4. pp. 5981-5996.

RIS

TY - JOUR

T1 - The COMBS Survey - II. Distinguishing the metal-poor bulge from the halo interlopers

AU - Lucey, Madeline

AU - Hawkins, Keith

AU - Ness, Melissa

AU - Debattista, Victor P.

AU - Luna, Alice

AU - Asplund, Martin

AU - Bensby, Thomas

AU - Casagrande, Luca

AU - Feltzing, Sofia

AU - Freeman, Kenneth C.

AU - Kobayashi, Chiaki

AU - Marino, Anna F.

PY - 2021

Y1 - 2021

N2 - 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 decreasing metallicity 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 the metal-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.

AB - 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 decreasing metallicity 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 the metal-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.

KW - Galaxy: bulge

KW - Galaxy: evolution

KW - stars: kinematics and dynamics

KW - stars: Population II

U2 - 10.1093/mnras/stab003

DO - 10.1093/mnras/stab003

M3 - Review article

AN - SCOPUS:85100802365

VL - 501

SP - 5981

EP - 5996

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 1365-2966

IS - 4

ER -