Strömgren photometric metallicity map of the Magellanic Cloud stars using Gaia DR3–XP spectra

¹ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
² Indian Institute of Astrophysics, Koramangala II Block, Bangalore 560034, India
³ Institut für Physik und Astronomie, Universität Potsdam, Haus 28, Karl-Liebknecht-Str. 24/25, D-14476 Potsdam, Germany
⁴ ESA, European Space Research and Technology Centre, Keplerlaan 1, 2201 AZ, Noordwijk, The Netherlands
⁵ Instituto de Astronomia y Ciencias Planetarias, Univeridad de Atacama, Copayapu 485, Copiapo, Chile
⁶ Instituto de Astrofísica, Departamento de Física y Astronomía, Facultad de Ciencias Exactas, Universidad Andres Bello, Fernandez Concha, 700, Las Condes, Santiago, Chile

^⋆ Corresponding author: aomkumar@aip.de

Received: 7 October 2024
Accepted: 4 June 2025

Abstract

Context. One key to understanding a galaxy’s evolution is studying the consequences of its past dynamical interactions that have influenced its shape. By measuring the metallicity distribution of stellar populations with different ages, one can learn about these interactions. The Magellanic Clouds, being the nearest pair of interacting dwarf galaxies with a morphology characterised by different tidal and kinematic sub-structures as well as a vast range of stellar populations, represent an excellent place to study the consequences of dwarf-dwarf galaxy interactions and the interactions with their large host, the Milky Way.

Aims. We aim to determine the metallicities ([Fe/H]) of red giant branch (old) and supergiant (young) stars covering the entire galaxies, estimate their radial metallicity gradients, and produce homogeneous metallicity maps.

Methods. We used the XP spectra from Gaia Data Release 3 to calculate synthetic Strömgren magnitudes from the application of the GaiaXPy tool and adopted calibration relations from the literature to estimate the photometric metallicities.

Results. We present photometric metallicity maps for ∼90 000 young stars and ∼270 000 old stars within ∼11 deg of the Small Magellanic Cloud and ∼20 deg of the Large Magellanic Cloud from a homogeneous dataset. We find that the overall radial metallicity gradients decrease linearly, in agreement with previous studies. Thanks to the large stellar samples, we could apply piecewise-regression fitting to derive the gradients within different radial regions. The catalogues containing the estimated photometric metallicities from this work are made available at the CDS.

Conclusions. The overall metallicity gradients, traced by young and old stars, decrease from the centre to the outskirts of both galaxies. However, they show multiple breakpoints, depicting regions following different and sometimes opposite trends. These are associated with the structure of the galaxies and their history of star formation and chemical evolution but may be influenced by a low number of sources, especially at the centre (due to crowding) and in the outermost regions.