The Pristine Inner Galaxy Survey (PIGS)

XI. Revealing the chemical evolution of the interacting Sagittarius dwarf galaxy^★

¹ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
² Millennium Nucleus ERIS, Chile
³ Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 82-0436 Macul, Santiago, Chile
⁴ Departamento de Física, Universidad de Santiago de Chile, Av. Victor Jara 3659, Santiago, Chile
⁵ Center for Interdisciplinary Research in Astrophysics and Space Exploration (CIRAS), Universidad de Santiago de Chile, Santiago, Chile
⁶ Centre for Astrophysics Research, Department of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield AL10 9AB, UK
⁷ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France
⁸ Instituto de Astrofísica de Canarias (IAC), Vía Láctea, 38205 La Laguna, Tenerife, Spain
⁹ Universidad de La Laguna, Dept. Astrofísica, 38206 La Laguna, Tenerife, Spain
¹⁰ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹¹ Laboratoire d’astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), 1290 Versoix, Switzerland
¹² Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
¹³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁴ Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands

^★★ Corresponding author: sara.vitali@mail.udp.cl

Received: 9 December 2024
Accepted: 14 May 2025

Abstract

Context. The Sagittarius dwarf spheroidal galaxy (Sgr dSph) is a satellite orbiting the Milky Way that has experienced multiple stripping events due to tidal interactions with our Galaxy. Its accretion history has led to a distinct stellar overdensity, which is the remnant of the core of the progenitor.

Aims. We present a complete chemical analysis of 111 giant stars in the core of Sgr dSph to investigate the chemical evolution and enrichment history of this satellite.

Methods. Employing the metallicity-sensitive Ca H&K photometry from the Pristine Inner Galaxy Survey, we selected stars that span a wide metallicity range and obtained high-resolution spectra with the ESO FLAMES/GIRAFFE multiobject spectrograph. For the stellar sample covering − 2.13 < [Fe/H] < − 0.35, we derived abundances for up to 14 chemical elements with average uncertainties of ∼ 0.09 dex and a set of stellar ages that allowed us to build an age-metallicity relation (AMR) for the entire sample.

Results. With the most comprehensive set of chemical species measured for the core of Sgr (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ba, La, and Eu), we studied several [X/Fe] ratios. Most trends align closely with Galactic chemical trends, but notable differences emerge in the heavy n-capture elements, which offer independent insights into the star formation history of a stellar population.

Conclusions. The deficiency in α elements with respect to the Milky Way suggests a slower, less efficient early star formation history, similar to other massive satellites. S -process element patterns indicate significant enrichment from Asymptotic giant branch stars over time. The AMR and chemical ratios point to an extended star formation history, with a rapid early phase in the first gigayears, followed by declining activity and later star-forming episodes. These findings are consistent with Sgr hosting multiple stellar populations, from young (∼4 Gyr) to old, metal-poor stars (∼10 Gyr).