Chemical abundances in the Milky Way's nuclear stellar disc

¹ Division of Astrophysics, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
² Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263002, India
³ Max Planck Institute for Astronomy, 69117 Heidelberg, Germany
⁴ Fakultät für Physik und Astronomie, Universität Heidelberg, Im Neuenheimer Feld 226, 69120 Heidelberg, Germany
⁵ Université Côte d’Azur, Observatoire de la Côte d’Azur, Laboratoire Lagrange, CNRS, Blvd de l’Observatoire, 06304 Nice, France
⁶ Departamento de Física, Universidad de Santiago de Chile, Av. Victor Jara 3659, Santiago, Chile
⁷ Millennium Institute of Astrophysics, Avenida Vicuña Mackenna 4860, Macul, Santiago 82-0436, Chile
⁸ Center for Interdisciplinary Research in Astrophysics and Space Exploration (CIRAS), Universidad de Santiago de Chile, Santiago, Chile
⁹ Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile

^★ Corresponding author: nils.ryde@fysik.lu.se

Received: 27 March 2025
Accepted: 21 May 2025

Abstract

Context. The nuclear stellar disc (NSD) is a rotating, disc-like structure in the Galactic centre; it is believed to have a distinct star formation history and a predominantly old stellar population. However, its formation history and evolutionary links to other structures in the Galactic centre remain uncertain. Studying the chemical evolution of the NSD could provide new insights into this region and key epochs in the Milky Way’s evolution, yet such studies remain rare.

Aims. We created the first comprehensive chemical census of the NSD by deriving abundance trends for 18 elements in nine M giants in the metallicity range −1.0 <[Fe/H]< +0.5. By comparing these trends with those of other Galactic populations – including the nuclear star cluster (NSC), the inner bulge, and the thin and thick discs – we seek to understand the chemical relationships between these structures.

Methods. To mitigate the extreme optical extinction along the line of sight, we obtained high-resolution H- and Ks-band spectra of NSD stars using the IGRINS spectrometer mounted on the Gemini South telescope. The observed M giants and stars from comparison populations were analysed in an consistent manner to minimise systematic uncertainties.

Results. The abundance trends of NSD stars exhibit strong similarities with those of the inner-bulge and NSC populations across a broad range of elements with different chemical evolution histories. The trends for α elements, Al, Cr, Mn, Co, Ni, Cu, Zn, and neutron-capture elements align closely with the local thick-disc behaviour at sub-solar metallicities. At super-solar metallicities, most elements follow the NSC and inner-bulge trends. Sodium is the only element exhibiting a distinct trend, with enhanced abundances in the NSD and NSC compared to both thin-disc and inner-bulge stars.

Conclusions. The chemical similarity of most of the 18 elements investigated, including Na, suggests that the NSD likely shares an evolutionary history with the NSC, and possibly with the inner-disc sequence. Further studies are required to determine potential evolutionary links to the complex stellar system Liller 1 and metal-rich globular clusters. We find no evidence of typical globular cluster abundance signatures in our NSD stars with sub-solar metallicities. Our study demonstrates the feasibility of obtaining high-quality abundance data even in highly dust-obscured regions of the Milky Way, paving the way for future surveys.