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.

doi:10.1093/mnras/stab003

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

Journal Article · Wed Jan 06 00:00:00 EST 2021 · Monthly Notices of the Royal Astronomical Society

DOI:https://doi.org/10.1093/mnras/stab003· OSTI ID:1850373

^[1]; ^[2]; Ness, Melissa ^[3]; ^[4]; Luna, Alice ^[2]; Asplund, Martin ^[5]; Bensby, Thomas ^[6]; ^[7]; ^[6]; Freeman, Kenneth C. ^[7]; Kobayashi, Chiaki ^[8]; ^[9]

Univ. of Texas, Austin, TX (United States); University of Texas at Austin
Univ. of Texas, Austin, TX (United States)
Flatiron Institute, New York, NY (United States). Columbia University, New York, NY (United States)
University of Central Lancashire, Preston (United Kingdom)
Max Planck Institute for Astrophysics (Germany)
Lund Observatory (Sweden)
The Australian National University, Canberra (Australia)
Univ. of Hertfordshire, Hatfield (United Kingdom)
Univ. di Padova, Padua (Italy); Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Padova, Padua (Italy); Centro di Ateneo di Studi e Attivita’ Spaziali ‘Giuseppe Colombo’ - CISAS, Padua (Italy)

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 percent 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.

View Accepted Manuscript (DOE)

Research Organization:: Univ. of Texas, Austin, TX (United States)

Sponsoring Organization:: National Science Foundation (NSF); Science and Technology Facility Council (STFC); UK Science and Technology Facility Council (STFC); USDOE National Nuclear Security Administration (NNSA)

Grant/Contract Number:: NA0003843

OSTI ID:: 1850373

Journal Information:: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 4 Vol. 501; ISSN 0035-8711

Publisher:: Oxford University PressCopyright Statement

Country of Publication:: United States

Language:: English

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The effects of age on red giant metallicities derived from the near-infrared Ca II triplet Cole, A. A.; Smecker-Hane, T. A.; Tolstoy, E. Monthly Notices of the Royal Astronomical Society, Vol. 347, Issue 2 https://doi.org/10.1111/j.1365-2966.2004.07223.x	journal	January 2004
On the nature of bulges in general and of box/peanut bulges in particular: input from N -body simulations Athanassoula, E. Monthly Notices of the Royal Astronomical Society, Vol. 358, Issue 4 https://doi.org/10.1111/j.1365-2966.2005.08872.x	journal	April 2005
Analysis and calibration of Ca ii triplet spectroscopy of red giant branch stars from VLT/FLAMES observations: Calibration of Ca ii triplet spectroscopy Battaglia, G.; Irwin, M.; Tolstoy, E. Monthly Notices of the Royal Astronomical Society, Vol. 383, Issue 1 https://doi.org/10.1111/j.1365-2966.2007.12532.x	journal	December 2007
Local stellar kinematics from RAVE data - I. Local standard of rest: LSR from RAVE DR3 Coşkunoğlu, B.; Ak, S.; Bilir, S. Monthly Notices of the Royal Astronomical Society https://doi.org/10.1111/j.1365-2966.2010.17983.x	journal	January 2011
Mining the Galactic halo for very metal-poor stars: Very metal-poor stars Salvadori, S.; Ferrara, A.; Schneider, R. Monthly Notices of the Royal Astronomical Society: Letters, Vol. 401, Issue 1 https://doi.org/10.1111/j.1745-3933.2009.00772.x	journal	January 2010
The Galaxy in Context: Structural, Kinematic, and Integrated Properties Bland-Hawthorn, Joss; Gerhard, Ortwin Annual Review of Astronomy and Astrophysics, Vol. 54, Issue 1 https://doi.org/10.1146/annurev-astro-081915-023441	journal	September 2016
Mesa Isochrones and Stellar Tracks (Mist). i. Solar-Scaled Models Choi, Jieun; Dotter, Aaron; Conroy, Charlie The Astrophysical Journal, Vol. 823, Issue 2 https://doi.org/10.3847/0004-637X/823/2/102	journal	May 2016
Mesa Isochrones and Stellar Tracks (Mist) 0: Methods for the Construction of Stellar Isochrones Dotter, Aaron The Astrophysical Journal Supplement Series, Vol. 222, Issue 1 https://doi.org/10.3847/0067-0049/222/1/8	journal	January 2016
Estimating Distance from Parallaxes. IV. Distances to 1.33 Billion Stars in Gaia Data Release 2 Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M. The Astronomical Journal, Vol. 156, Issue 2 https://doi.org/10.3847/1538-3881/aacb21	journal	July 2018
The Bulge Radial Velocity Assay for RR Lyrae Stars (BRAVA-RR) DR2: A Bimodal Bulge? Kunder, Andrea; Pérez-Villegas, Angeles; Rich, R. Michael The Astronomical Journal, Vol. 159, Issue 6 https://doi.org/10.3847/1538-3881/ab8d35	journal	May 2020
The Sixth Data Release of the Radial Velocity Experiment (Rave). II. Stellar Atmospheric Parameters, Chemical Abundances, and Distances Steinmetz, Matthias; Guiglion, Guillaume; McMillan, Paul J. The Astronomical Journal, Vol. 160, Issue 2 https://doi.org/10.3847/1538-3881/ab9ab8	journal	July 2020
The Sixth Data Release of the Radial Velocity Experiment (RAVE). I. Survey Description, Spectra, and Radial Velocities Steinmetz, Matthias; Matijevič, Gal; Enke, Harry The Astronomical Journal, Vol. 160, Issue 2 https://doi.org/10.3847/1538-3881/ab9ab9	journal	July 2020
The Most Metal-poor Stars in the Inner Bulge Reggiani, Henrique; Schlaufman, Kevin C.; Casey, Andrew R. The Astronomical Journal, Vol. 160, Issue 4 https://doi.org/10.3847/1538-3881/aba948	journal	September 2020
Farthest Neighbor: The Distant Milky Way Satellite Eridanus II Li, T. S.; Simon, J. D.; Drlica-Wagner, A. The Astrophysical Journal, Vol. 838, Issue 1 https://doi.org/10.3847/1538-4357/aa6113	journal	March 2017
The Bulge Metallicity Distribution from the APOGEE Survey García Pérez, Ana E.; Ness, Melissa; Robin, Annie C. The Astrophysical Journal, Vol. 852, Issue 2 https://doi.org/10.3847/1538-4357/aa9d88	journal	January 2018
The Chemical Composition of NGC 5824, a Globular Cluster without Iron Spread but with an Extreme Mg–Al Anticorrelation Mucciarelli, Alessio; Lapenna, Emilio; Ferraro, Francesco R. The Astrophysical Journal, Vol. 859, Issue 1 https://doi.org/10.3847/1538-4357/aaba80	journal	May 2018
Evidence for the Third Stellar Population in the Milky Way’s Disk Carollo, Daniela; Chiba, Masashi; Ishigaki, Miho The Astrophysical Journal, Vol. 887, Issue 1 https://doi.org/10.3847/1538-4357/ab517c	journal	December 2019
Before the bar: Kinematic Detection of a Spheroidal Metal-Poor Bulge Component Kunder, Andrea; Rich, R. M.; Koch, A. The Astrophysical Journal, Vol. 821, Issue 2 https://doi.org/10.3847/2041-8205/821/2/L25	journal	April 2016
The Splash without a Merger Amarante, João A. S.; Beraldo e. Silva, Leandro; Debattista, Victor P. The Astrophysical Journal, Vol. 891, Issue 2 https://doi.org/10.3847/2041-8213/ab78a4	journal	March 2020

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