Searching for a kinematic signature of the moderately metal-poor stars in the Milky Way bulge using N-body simulations

Gómez, A.; Matteo, P. Di; Schultheis, M.; Fragkoudi, Francesca; Haywood, M.; Combes, F.

doi:10.1051/0004-6361/201732568

Cited by 12 publications

(5 citation statements)

References 79 publications

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“…It is also a phenomenology observed in external local galaxies with central B/P bar-dominated morphologies (Molaeinezhad et al 2016). The slightly enhanced rotation pattern towards the midplane observed in our data represents an additional signature of bar-dominated dynamics (Gómez et al 2018). The σ(V GC ) maps (Fig.…”

Section: The Bulge's Mdf In the Context Of Bulge Formation Mechanisms...supporting

confidence: 79%

How Many Components? Quantifying the Complexity of the Metallicity Distribution in the Milky Way Bulge with APOGEE

Rojas-Arriagada,

Zasowski,

Schultheis

et al. 2020

Preprint

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We use data of ∼13.000 stars from the SDSS/APOGEE survey to study the shape of the MDF within the region |l| ≤ 11 • and |b| ≤ 13 • , and spatially constrained to R GC ≤ 3.5 kpc. We apply Gaussian Mixture Modeling (GMM) and Non-negative Matrix Factorization (NMF) decomposition techniques to identify the optimal number and the properties of MDF components in different spatial locations and under different sampling conditions. We find the shape and spatial variations of the MDF (at [Fe/H] ≥ −1 dex) are well represented as a smoothly varying contribution of three overlapping components located at [Fe/H] =+0.32, −0.17 and −0.66 dex. The bimodal MDF found in previous studies is in agreement with our trimodal assessment once the limitations in sample size and individual measurement errors are taken into account. The shape of the MDF and its correlations with kinematics reveal different spatial distributions and kinematical profiles for the three chemical components co-existing in the bulge region. We confirm the consensus physical interpretation of metal-rich stars as associated with the boxy/peanut X-shape bar, originating from the secular evolution of the early disc. On the other hand, metal-intermediate stars could be the product of in-situ formation at high redshift, in a gas-rich environment characterized by violent and fast star formation. This interpretation would help to link a present-day structure with those observed in formation in the center of high redshift galaxies. We refrain from associating the metal-poor stars with any particular formation mechanism. They seem to be inconsistent with being thick disc or halo stars, but may be the metal-rich tail of the population currently being characterized at lower metallicity from the study of RR Lyrae stars. Conversely, they could be associated with the metal-poor tail of the early thick disc.

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Section: The Bulge's Mdf In the Context Of Bulge Formation Mechanisms...supporting

confidence: 79%

How Many Components? Quantifying the Complexity of the Metallicity Distribution in the Milky Way Bulge with APOGEE

Rojas-Arriagada,

Zasowski,

Schultheis

et al. 2020

Preprint

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“…These studies also determined that the metal-poor bulge stars rotate slower than the metalrich stars, which may indicate different origins. However, using N-body simulations, Gómez et al (2018) demonstrate that a classical bulge population would show even slower rotation than what has been observed among metal-poor bulge stars and that the observations can be explained by a thick disk component. Nevertheless, it is unclear how many, if any of these stars in previous studies are confined bulge stars rather than halo interlopers which are just passing through the bulge.…”

Section: Discussionmentioning

confidence: 81%

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

Lucey

Hawkins

Ness

et al. 2021

Monthly Notices of the Royal Astronomical Society

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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.

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“…While some of the trends explored in this work can also be explained by a massive classical bulge, a number of works have shown that such a massive spheroid cannot explain the kinematic trends of these stellar populations (e.g. Shen et al 2010;Kunder et al 2012;Di Matteo et al 2015;Gómez et al 2018). On the other hand, as we will show in a subsequent paper of this series (Di Matteo et al, in prep.…”

Section: Discussionmentioning

confidence: 85%

The disc origin of the Milky Way bulge

Fragkoudi

Matteo

Haywood

et al. 2018

A&A

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There is a long-standing debate over the origin of the metal-poor stellar populations of the Milky Way (MW) bulge, with the two leading scenarios being that these populations are either (i) part of a classical metal-poor spheroid or (ii) the same population as the chemically defined thick disc seen at the solar neighbourhood. Here we test whether the latter scenario can reproduce the observed chemical properties of the MW bulge. To do so we compare an N-body simulation of a composite (thin+thick) stellar disc – which evolves secularly to form a bar and a boxy/peanut (b/p) bulge – to data from APOGEE DR13. This model, in which the thick disc is massive and centrally concentrated, can reproduce the morphology of the metal-rich and metal-poor stellar populations in the bulge, as well as the mean metallicity and [α/Fe] maps as obtained from the APOGEE data. It also reproduces the trends, in both longitude and latitude, of the bulge metallicity distribution function (MDF). Additionally, we show that the model predicts small but measurable azimuthal metallicity variations in the inner disc due to the differential mapping of the thin and thick disc in the bar. We therefore see that the chemo-morphological relations of stellar populations in the MW bulge are naturally reproduced by mapping the thin and thick discs of the inner MW into a b/p.

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Searching for a kinematic signature of the moderately metal-poor stars in the Milky Way bulge using N-body simulations

Cited by 12 publications

References 79 publications

How Many Components? Quantifying the Complexity of the Metallicity Distribution in the Milky Way Bulge with APOGEE

How Many Components? Quantifying the Complexity of the Metallicity Distribution in the Milky Way Bulge with APOGEE

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

The disc origin of the Milky Way bulge

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