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, T.; Casagrande, Luca; Feltzing, Sofia; Freeman, K. C.; Marino, A. F.

doi:10.1093/mnras/stab003

Cited by 31 publications

(29 citation statements)

References 118 publications

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“…As the stars in the [Fe/H]-poor tail are slowly rotating, kinematically hot, and [Mg/Fe]-rich, we tentatively associate them with the stellar halo. A contamination by halo stars is further supported by Lucey et al (2021) who, from examining the chemo-kinematics of metal poor bulge stars, found that the fraction of halo interlopers in the bulge increases with decreasing metallicity between −3 < [Fe/H] (dex) < 0.5. In all, our data paints a consistent picture for the origin of the b/p bulge: at least two initial disks with differing dispersions, scale heights, and scale lengths underwent spatial and kinematic fractionation resulting in the b/p bulge of the Milky Way that we observe today.…”

Section: Kinematics Withmentioning

confidence: 76%

A2A: 21,000 bulge stars from the ARGOS survey with stellar parameters on the APOGEE scale

Wylie,

Gerhard,

Ness

et al. 2021

Preprint

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Aims. Spectroscopic surveys have by now collectively observed tens of thousands of stars in the bulge of our Galaxy. However, each of these surveys had unique observing and data processing strategies which led to distinct stellar parameter and abundance scales. Because of this, stellar samples from different surveys cannot be directly combined. Methods. Here we use the data-driven method, The Cannon, to bring 21,000 stars from the argos bulge survey, including 10,000 red clump stars, onto the parameter and abundance scales of the cross-Galactic survey, apogee, obtaining rms precisions of 0.10 dex, 0.07 dex, 74 K, and 0.18 dex for [Fe/H], [Mg/Fe], T eff , and log(g), respectively. The re-calibrated argos survey -which we refer to as the a2a survey -is combined with the APOGEE survey to investigate the abundance structure of the Galactic bulge. Results. We find X-shaped [Fe/H] and [Mg/Fe] distributions in the bulge that are more pinched than the bulge density, a signature of its disk origin. The mean abundance along the major axis of the bar varies such that the stars are more [Fe/H]-poor and [Mg/Fe]rich near the Galactic center than in the long bar/outer bulge region. The vertical [Fe/H] and [Mg/Fe] gradients vary between the inner bulge and long bar with the inner bulge showing a flattening near the plane that is absent in the long bar. The [Fe/H]-[Mg/Fe] distribution shows two main maxima, an "[Fe/H]-poor [Mg/Fe]-rich" maximum and an "[Fe/H]-rich [Mg/Fe]-poor" maximum, that vary in strength with position in the bulge. In particular, the outer long bar close to the Galactic plane is dominated by super-solar [Fe/H], [Mg/Fe]-normal stars. Stars composing the [Fe/H]-rich maximum show little kinematic dependence on [Fe/H], but for lower [Fe/H] the rotation and dispersion of the bulge increase slowly. Stars with [Fe/H] < −1 dex have a very different kinematic structure than stars with higher [Fe/H]. Conclusions. Comparing with recent models for the Galactic boxy-peanut bulge, the abundance gradients and distribution, and the relation between [Fe/H] and kinematics suggest that the stars comprising each maximum have separate disk origins with the "[Fe/H]poor [Mg/Fe]-rich" stars originating from a thicker disk than the "[Fe/H]-rich [Mg/Fe]-poor" stars.

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Section: Kinematics Withmentioning

confidence: 76%

A2A: 21,000 bulge stars from the ARGOS survey with stellar parameters on the APOGEE scale

Wylie,

Gerhard,

Ness

et al. 2021

Preprint

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Section: Kinematics With Metallicity Along the [Fementioning

confidence: 77%

A2A: 21 000 bulge stars from the ARGOS survey with stellar parameters on the APOGEE scale

Wylie

Gerhard

Ness

et al. 2021

A&A

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Aims. Spectroscopic surveys have by now collectively observed tens of thousands of stars in the bulge of our Galaxy. However, each of these surveys had unique observing and data processing strategies that led to distinct stellar parameter and abundance scales. Because of this, stellar samples from different surveys cannot be directly combined. Methods. Here we use the data-driven method, The Cannon, to bring 21 000 stars from the ARGOS bulge survey, including 10 000 red clump stars, onto the parameter and abundance scales of the cross-Galactic survey, APOGEE, obtaining rms precisions of 0.10 dex, 0.07 dex, 74 K, and 0.18 dex for [Fe/H], [Mg/Fe], Teff, and log(g), respectively. The re-calibrated ARGOS survey – which we refer to as the A2A survey – is combined with the APOGEE survey to investigate the abundance structure of the Galactic bulge. Results. We find X-shaped [Fe/H] and [Mg/Fe] distributions in the bulge that are more pinched than the bulge density, a signature of its disk origin. The mean abundance along the major axis of the bar varies such that the stars are more [Fe/H]-poor and [Mg/Fe]-rich near the Galactic centre than in the outer bulge and the long bar region. The vertical [Fe/H] and [Mg/Fe] gradients vary between the inner bulge and the long bar, with the inner bulge showing a flattening near the plane that is absent in the long bar. The [Fe/H] − [Mg/Fe] distribution shows two main maxima, an ‘[Fe/H]-poor [Mg/Fe]- rich’ maximum and an ‘[Fe/H]-rich [Mg/Fe]-poor’ maximum, that vary in strength with position in the bulge. In particular, the outer long bar close to the Galactic plane is dominated by super-solar [Fe/H], [Mg/Fe]-normal stars. Stars composing the [Fe/H]-rich maximum show little kinematic dependence on [Fe/H], but for lower [Fe/H] the rotation and dispersion of the bulge increase slowly. Stars with [Fe/H] < −1 dex have a very different kinematic structure than stars with higher [Fe/H]. Conclusions. Comparing with recent models for the Galactic boxy-peanut bulge, the abundance gradients and distribution, and the relation between [Fe/H] and kinematics suggests that the stars comprising each maximum have separate disk origins with the ‘[Fe/H]-poor [Mg/Fe]-rich’ stars originating from a thicker disk than the ‘[Fe/H]-rich [Mg/Fe]-poor’ stars.

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“…However, some stars are potentially simply passing through the inner regions on highly elliptical orbits with large apocentres and are thus not truly inner Galaxy stars. It is still unclear how many of the metal-poor stars currently in the inner Galaxy are halo interlopers, with estimates ranging from 25 to 75 per cent (Howes et al 2015;Kunder et al 2020;Lucey et al 2021). It is desirable to have orbital information of all the stars in PIGS to be able to select a true inner Galaxy sample.…”

Section: Future Workmentioning

confidence: 99%

“…Metal-poor stars are highly outnumbered by metal-rich stars, and dust extinction obstructs and disturbs our view. However, thanks to efficient pre-selection methods and/or large surveys, the number of very metal-poor (VMP) inner Galaxy stars identified and studied has been increasing in recent years (Ness et al 2013;García Pérez et al 2013;Howes et al 2014Howes et al , 2015Howes et al , 2016Casey & Schlaufman 2015;Koch et al 2016;Lamb et al 2017;Lucey et al 2019Lucey et al , 2021Reggiani et al 2020;Arentsen et al 2020b).…”

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confidence: 99%

The Pristine Inner Galaxy Survey (PIGS) III: carbon-enhanced metal-poor stars in the bulge

Arentsen

Starkenburg

Aguado

et al. 2021

Monthly Notices of the Royal Astronomical Society

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The most metal-deficient stars hold important clues about the early build-up and chemical evolution of the Milky Way, and carbon-enhanced metal-poor (CEMP) stars are of special interest. However, little is known about CEMP stars in the Galactic bulge. In this paper, we use the large spectroscopic sample of metal-poor stars from the Pristine Inner Galaxy Survey (PIGS) to identify CEMP stars ($\rm {[C/Fe]} \geqslant +0.7$) in the bulge region and to derive a CEMP fraction. We identify 96 new CEMP stars in the inner Galaxy, of which 62 are very metal-poor ($\rm {[Fe/H]} < -2.0$); this is more than a ten-fold increase compared to the seven previously known bulge CEMP stars. The cumulative fraction of CEMP stars in PIGS is $42^{\, +14\, }_{\, -13} {{\ \rm per\ cent}}$ for stars with $\rm {[Fe/H]} < -3.0$, and decreases to $16^{\, +3\, }_{\, -3} {{\ \rm per\ cent}}$ for $\rm {[Fe/H]} < -2.5$ and $5.7^{\, +0.6\, }_{\, -0.5} {{\ \rm per\ cent}}$ for $\rm {[Fe/H]} < -2.0$. The PIGS inner Galaxy CEMP fraction for $\rm {[Fe/H]} < -3.0$ is consistent with the halo fraction found in the literature, but at higher metallicities the PIGS fraction is substantially lower. While this can partly be attributed to a photometric selection bias, such bias is unlikely to fully explain the low CEMP fraction at higher metallicities. Considering the typical carbon excesses and metallicity ranges for halo CEMP-s and CEMP-no stars, our results point to a possible deficiency of both CEMP-s and CEMP-no stars (especially the more metal-rich) in the inner Galaxy. The former is potentially related to a difference in the binary fraction, whereas the latter may be the result of a fast chemical enrichment in the early building blocks of the inner Galaxy.

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

Cited by 31 publications

References 118 publications

A2A: 21,000 bulge stars from the ARGOS survey with stellar parameters on the APOGEE scale

A2A: 21,000 bulge stars from the ARGOS survey with stellar parameters on the APOGEE scale

A2A: 21 000 bulge stars from the ARGOS survey with stellar parameters on the APOGEE scale

The Pristine Inner Galaxy Survey (PIGS) III: carbon-enhanced metal-poor stars in the bulge

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