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

Abstract

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. 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. 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. 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. 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.

Accepted for publication in A&A. 11 pages, 12 figures

References in corpus (30)

• Detection of the Schwarzschild precession in the orbit of the star S2 near the Galactic centre massive black hole
• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• The Structure of the Milky Way's Bar Outside the Bulge
• The old nuclear star cluster in the Milky Way: dynamics, mass, statistical parallax, and black hole mass
• Interstellar Extinction Law toward the Galactic Center II: V, J, H, and Ks Bands
• Wild at Heart:-The Particle Astrophysics of the Galactic Centre
• Extinction ratios in the inner Galaxy as revealed by the VVV survey
• Mass inflow rate into the Central Molecular Zone: observational determination and evidence of episodic accretion
• Henize 2-10: the ongoing formation of a nuclear star cluster around a massive black hole
• On the rotation of nuclear star clusters formed by cluster-inspirals
• New constraints on the structure of the nuclear stellar cluster of the Milky Way from star counts and MIR imaging
• The Milky Way's nuclear stellar disc: A dynamically cool and metal-rich component formed from the Central Molecular Zone?
• Proper Motion Dispersions of Red Clump Giants in the Galactic Bulge: Observations and Model Comparisons
• Transverse kinematics of the Galactic bar-bulge from VVV and Gaia
• Mapping stellar kinematics across the Galactic bar: HST measurements of proper motions in 35 fields
• Interstellar Extinction and Long-Period Variables in the Galactic Center
• Mapping the stellar age of the Milky Way bulge with the VVV. I. The method
• On the origin of a rotating metal-poor stellar population in the Milky Way Nuclear Cluster
• GALACTICNUCLEUS: A high-angular-resolution $JH{K}_s$ imaging survey of the Galactic centre. IV. Extinction maps and de-reddened photometry
• Chemical evolution of the Galactic Center
• Mira variables in the Milky Way's nuclear stellar disc: discovery and classification
• The extinction law in the inner $3\times 3$ deg${}^2$ of the Milky Way and the red clump absolute magnitude in the inner bar-bulge
• A proper motion catalogue for the Milky Way's nuclear stellar disc
• The formation history of our Galaxy's nuclear stellar disc constrained from HST observations of the Quintuplet field
• Evidence of an age gradient along the line of sight in the nuclear stellar disc of the Milky Way
• Kinematic data rebuild the Nuclear star cluster as the most metal rich region of the Galaxy
• A first glimpse at the line-of-sight structure of the Milky Way's nuclear stellar disc
• Position and Proper Motion of Sagittarius A* in the ICRF3 Frame from VLBI Absolute Astrometry
• Distance to the Brick cloud using stellar kinematics
• Smooth kinematic and metallicity gradients reveal that the Milky Way's nuclear star cluster and disc might be part of the same structure

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