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Chemical analysis of the Milky Way's nuclear star cluster : Evidence for a metallicity gradient

Schultheis, M. ; Serrano, L. ; Thorsbro, B. LU orcid ; Nogueras-Lara, F. ; Feldmeier-Krause, A. ; Nandakumar, G. LU ; Fiteni, K. ; Sormani, M. C. and Ryde, N. LU orcid (2026) In Astronomy and Astrophysics 705.
Abstract

Context. The Milky Way nuclear star cluster (MWNSC) is located in the Galactic centre, together with the Milky Way nuclear stellar disc (MWNSD), and they dominate the gravitational potential within the inner 300 pc. However, the formation and evolution of the two systems and their possible connections are still under debate. Aims. We reanalysed the low-resolution KMOS spectra in the MWNSC with the aim of improving the stellar parameters (Teff, log g, and [M/H]) for the MWNSC. Methods. We used an improved line list, especially dedicated for cool M giants, that allowed us to improve the stellar parameters and to obtain in addition global α-elements. A comparison with high-resolution IR spectra (from IGRINS) gives very... (More)

Context. The Milky Way nuclear star cluster (MWNSC) is located in the Galactic centre, together with the Milky Way nuclear stellar disc (MWNSD), and they dominate the gravitational potential within the inner 300 pc. However, the formation and evolution of the two systems and their possible connections are still under debate. Aims. We reanalysed the low-resolution KMOS spectra in the MWNSC with the aim of improving the stellar parameters (Teff, log g, and [M/H]) for the MWNSC. Methods. We used an improved line list, especially dedicated for cool M giants, that allowed us to improve the stellar parameters and to obtain in addition global α-elements. A comparison with high-resolution IR spectra (from IGRINS) gives very satisfactory results and constrains the uncertainties to Teff ≃ 150 K, log g ≃ 0.4 dex, and [M/H] ≃ 0.2 dex. Our α-elements agree within 0.1 dex compared to the IGRINS spectra. Results. We obtained a high-quality sample of 1140 M giant stars where we see an important contribution of a metal-poor population (∼20%) centred at [M/H] ≃ -0.7 dex, while the most dominant part comes from the metal-rich population with [M/H] ≃ 0.26 dex. We constructed a metallicity map and find a metallicity gradient of ∼-0.1 ± 0.02 dex/pc favouring the inside-out formation scenario for the MWNSC.

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author
; ; ; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Galaxy: abundances, Galaxy: center, Galaxy: nucleus, Galaxy: stellar content, Stars: abundances, Stars: late-type
in
Astronomy and Astrophysics
volume
705
article number
A235
publisher
EDP Sciences
external identifiers
  • scopus:105028912568
ISSN
0004-6361
DOI
10.1051/0004-6361/202557723
language
English
LU publication?
yes
id
dec1172b-e62d-40af-9118-72b51cfab80a
date added to LUP
2026-02-23 15:48:48
date last changed
2026-02-23 15:49:08
@article{dec1172b-e62d-40af-9118-72b51cfab80a,
  abstract     = {{<p>Context. The Milky Way nuclear star cluster (MWNSC) is located in the Galactic centre, together with the Milky Way nuclear stellar disc (MWNSD), and they dominate the gravitational potential within the inner 300 pc. However, the formation and evolution of the two systems and their possible connections are still under debate. Aims. We reanalysed the low-resolution KMOS spectra in the MWNSC with the aim of improving the stellar parameters (T<sub>eff</sub>, log g, and [M/H]) for the MWNSC. Methods. We used an improved line list, especially dedicated for cool M giants, that allowed us to improve the stellar parameters and to obtain in addition global α-elements. A comparison with high-resolution IR spectra (from IGRINS) gives very satisfactory results and constrains the uncertainties to T<sub>eff</sub> ≃ 150 K, log g ≃ 0.4 dex, and [M/H] ≃ 0.2 dex. Our α-elements agree within 0.1 dex compared to the IGRINS spectra. Results. We obtained a high-quality sample of 1140 M giant stars where we see an important contribution of a metal-poor population (∼20%) centred at [M/H] ≃ -0.7 dex, while the most dominant part comes from the metal-rich population with [M/H] ≃ 0.26 dex. We constructed a metallicity map and find a metallicity gradient of ∼-0.1 ± 0.02 dex/pc favouring the inside-out formation scenario for the MWNSC.</p>}},
  author       = {{Schultheis, M. and Serrano, L. and Thorsbro, B. and Nogueras-Lara, F. and Feldmeier-Krause, A. and Nandakumar, G. and Fiteni, K. and Sormani, M. C. and Ryde, N.}},
  issn         = {{0004-6361}},
  keywords     = {{Galaxy: abundances; Galaxy: center; Galaxy: nucleus; Galaxy: stellar content; Stars: abundances; Stars: late-type}},
  language     = {{eng}},
  publisher    = {{EDP Sciences}},
  series       = {{Astronomy and Astrophysics}},
  title        = {{Chemical analysis of the Milky Way's nuclear star cluster : Evidence for a metallicity gradient}},
  url          = {{http://dx.doi.org/10.1051/0004-6361/202557723}},
  doi          = {{10.1051/0004-6361/202557723}},
  volume       = {{705}},
  year         = {{2026}},
}