Letter to the Editor

The formation history of our Galaxy’s nuclear stellar disc constrained from HST observations of the Quintuplet field

¹ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
e-mail: rainer@iaa.es
² European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
³ Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
⁴ Department of Astronomy, University of California, 501 Campbell Hall, Berkeley, CA 94720, USA

Received: 6 March 2023
Accepted: 31 March 2023

Abstract

Context. Until recently it was thought that the nuclear stellar disc at the centre of our Galaxy was formed via quasi-continuous star formation over billions of years. However, an analysis of GALACTICNUCLEUS survey data indicates that > 80% of the mass of the stellar disc formed at least 8 Gyr ago and about 5% roughly 1 Gyr ago.

Aims. Our aim is to derive new constraints on the formation history of the nuclear stellar disc.

Methods. We analysed a catalogue of HST/WFC3-IR observations of the Quintuplet cluster field. From this catalogue, we selected about 24 000 field stars that probably belong to the nuclear stellar disc. We used red clump giants to deredden the sample and fit the resulting F153M luminosity function with a linear combination of theoretical luminosity functions created from different stellar evolutionary models.

Results. We find that ≳70% of the stellar population in the nuclear disc probably formed more than 10 Gyr ago, while ∼15% formed in an event (or series of events) ∼1 Gyr ago. Up to 10% of the stars appear to have formed in the past tens to hundreds of Myr. These results do not change significantly for reasonable variations in the assumed mean metallicity, sample selection, reddening correction, or stellar evolutionary models.

Conclusions. We confirm previous work that changed the formation paradigm for stars in the Galactic Centre. The nuclear stellar disc is indeed a very old structure. There seems to have been little star formation activity between its formation and about 1 Gyr ago.