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Metallicity-dependent kinematics and orbits in the Milky Way's nuclear stellar disc

Nogueras-Lara, F. ; Nieuwmunster, N. LU ; Schultheis, M. ; Sormani, M. C. ; Fragkoudi, F. ; Thorsbro, B. LU orcid ; Rich, R. M. ; Ryde, N. LU orcid ; Sanders, J. L. and Smith, L. C. (2024) In Astronomy and Astrophysics 690.
Abstract

Context. The nuclear stellar disc (NSD) is a flat and dense stellar structure at the centre of the Milky Way. Previous work has identified the presence of metal-rich and metal-poor stars in the NSD, suggesting that they have different origins. The recent publication of photometric, metallicity, proper motion, and orbital catalogues allows the NSD stellar population to be characterised with unprecedented detail. Aims. We aim to explore the proper motions and orbits of NSD stars with different metallicities to assess whether they have different origins and to better understand the metallicity distribution in the NSD. Methods. We distinguished between metal-rich and metal-poor stars by applying a Gaussian mixture model, as done in previous... (More)

Context. The nuclear stellar disc (NSD) is a flat and dense stellar structure at the centre of the Milky Way. Previous work has identified the presence of metal-rich and metal-poor stars in the NSD, suggesting that they have different origins. The recent publication of photometric, metallicity, proper motion, and orbital catalogues allows the NSD stellar population to be characterised with unprecedented detail. Aims. We aim to explore the proper motions and orbits of NSD stars with different metallicities to assess whether they have different origins and to better understand the metallicity distribution in the NSD. Methods. We distinguished between metal-rich and metal-poor stars by applying a Gaussian mixture model, as done in previous work, and analysed the proper motions, orbits, and spatial distribution of stars with different metallicities. Results. We find that metal-rich stars exhibit a lower velocity dispersion, suggesting that they trace a kinematically cooler component compared to metal-poor ones. Furthermore, z-tube orbits are predominant among metal-rich stars, while chaotic/box orbits are more common among metal-poor ones. We also find that metal-rich and metal-poor stars show a similar extinction and are present throughout the analysed regions. As a secondary result, we detected a metallicity gradient in the metal-rich population with higher metallicity towards the centre of the NSD and a tentative gradient for the metal-poor stars, which is consistent with previous studies that did not distinguish between the two populations. Conclusions. Our results suggest that metal-rich stars trace the NSD, whereas metal-poor ones are related to the Galactic bar and probably constitute Galactic bar interlopers and/or are NSD stars that originated from accreted clusters. The detected metallicity gradients aligns with the currently accepted inside-out formation of the NSD.

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author
; ; ; ; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Galaxy: bulge, Galaxy: center, Galaxy: kinematics and dynamics, Galaxy: nucleus, Galaxy: stellar content, Galaxy: structure
in
Astronomy and Astrophysics
volume
690
article number
A313
publisher
EDP Sciences
external identifiers
  • scopus:85207459970
ISSN
0004-6361
DOI
10.1051/0004-6361/202450946
language
English
LU publication?
yes
additional info
Publisher Copyright: © The Authors 2024.
id
1a166ac7-5514-4ec7-ac64-3dd73f083b13
date added to LUP
2024-12-18 09:26:21
date last changed
2025-04-04 14:37:44
@article{1a166ac7-5514-4ec7-ac64-3dd73f083b13,
  abstract     = {{<p>Context. The nuclear stellar disc (NSD) is a flat and dense stellar structure at the centre of the Milky Way. Previous work has identified the presence of metal-rich and metal-poor stars in the NSD, suggesting that they have different origins. The recent publication of photometric, metallicity, proper motion, and orbital catalogues allows the NSD stellar population to be characterised with unprecedented detail. Aims. We aim to explore the proper motions and orbits of NSD stars with different metallicities to assess whether they have different origins and to better understand the metallicity distribution in the NSD. Methods. We distinguished between metal-rich and metal-poor stars by applying a Gaussian mixture model, as done in previous work, and analysed the proper motions, orbits, and spatial distribution of stars with different metallicities. Results. We find that metal-rich stars exhibit a lower velocity dispersion, suggesting that they trace a kinematically cooler component compared to metal-poor ones. Furthermore, z-tube orbits are predominant among metal-rich stars, while chaotic/box orbits are more common among metal-poor ones. We also find that metal-rich and metal-poor stars show a similar extinction and are present throughout the analysed regions. As a secondary result, we detected a metallicity gradient in the metal-rich population with higher metallicity towards the centre of the NSD and a tentative gradient for the metal-poor stars, which is consistent with previous studies that did not distinguish between the two populations. Conclusions. Our results suggest that metal-rich stars trace the NSD, whereas metal-poor ones are related to the Galactic bar and probably constitute Galactic bar interlopers and/or are NSD stars that originated from accreted clusters. The detected metallicity gradients aligns with the currently accepted inside-out formation of the NSD.</p>}},
  author       = {{Nogueras-Lara, F. and Nieuwmunster, N. and Schultheis, M. and Sormani, M. C. and Fragkoudi, F. and Thorsbro, B. and Rich, R. M. and Ryde, N. and Sanders, J. L. and Smith, L. C.}},
  issn         = {{0004-6361}},
  keywords     = {{Galaxy: bulge; Galaxy: center; Galaxy: kinematics and dynamics; Galaxy: nucleus; Galaxy: stellar content; Galaxy: structure}},
  language     = {{eng}},
  month        = {{10}},
  publisher    = {{EDP Sciences}},
  series       = {{Astronomy and Astrophysics}},
  title        = {{Metallicity-dependent kinematics and orbits in the Milky Way's nuclear stellar disc}},
  url          = {{http://dx.doi.org/10.1051/0004-6361/202450946}},
  doi          = {{10.1051/0004-6361/202450946}},
  volume       = {{690}},
  year         = {{2024}},
}