The nuclear star cluster and nuclear stellar disc of the Milky Way: Different stellar population and star formation history

Abstract

The Milky Way's nuclear stellar disc (NSD) and nuclear star cluster (NSC) are the main features of the Galactic centre. Nevertheless, their observation is hampered by the extreme source crowding and high extinction. Hence, their relation and formation scenario are not fully clear yet. We aim at detecting the stellar populations from the NSC and the NSD along the line-of-sight towards the NSC, and assess whether they have different stellar populations and star formation histories. We analysed the colour-magnitude diagram, $K_s$ vs. $H-K_s$, of a region of $8.2^{\prime }\times 2.8^{\prime }$ centred on the NSC, and detected two different stellar groups with different extinctions. We studied their red clumps to find the features associated to each of the stellar populations. We obtained that the two groups of stars correspond to the NSD and the NSC, and found that they have significantly different stellar populations and star formation histories. We detected a double red clump for the NSD population, in agreement with previous work, whereas the NSC presents a more complex structure well fitted by three Gaussian features. We created extinction maps to analyse the extinction variation between the detected stellar groups. We found that the high-extinction layer varies on smaller scales (arc-seconds), and that there is a difference of $A_{K_s}\sim 0.6$\,mag between both extinction layers. Finally, we obtained that the distance towards each of the stellar populations is compatible with the Galactic centre distance, and found some evidence of a slightly closer distance for the NSD stars ($\sim 360\pm 200$\,pc).

Accepted for publication in ApJ. 13 pages, 10 figures

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• 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
• Fluorine Abundances in the Galactic Nuclear Star Cluster
• The Origin of Stars in the Inner 500 Parsecs in TNG50 Galaxies
• A first glimpse at the line-of-sight structure of the Milky Way's nuclear stellar disc
• Evidence of Deep Mixing in IRS 7, a Cool Massive Supergiant Member of the Galactic Nuclear Star Cluster
• Smooth kinematic and metallicity gradients reveal that the Milky Way's nuclear star cluster and disc might be part of the same structure
• The LEGARE Project. I. Chemical evolution model of the Nuclear Stellar Disc in a Bayesian framework
• Chemical analysis of the Milky Way's Nuclear Star Cluster: Evidence for a metallicity gradient
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• The contribution to Galactic Centre γ-ray excess from cluster-born millisecond pulsars. Constraints from direct N-body simulations
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