The chemical DNA of the Magellanic Clouds

VI. Origin and evolution of neutron-capture elements in the SMC

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
² Dipartimento di Fisica e Astronomia ‘Augusto Righi’, Alma Mater Studiorum, Via Gobetti 93/2, 40129 Bologna, Italy
³ INAF, Osservatorio di Astrofisica e Scienza dello Spazio, Via Gobetti 93/3, 40129 Bologna, Italy
⁴ Dipartimento di Fisica, Sezione di Astronomia, Università di Trieste, Via G. B. Tiepolo 11, 34143 Trieste, Italy

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 17 December 2025
Accepted: 8 April 2026

Abstract

Context. In the context of galactic archaeology, the study of the Small Magellanic Cloud (SMC) is of crucial importance, as it represents a unique opportunity to study a nearby massive dwarf system. However, theoretical studies of the chemical evolution of this galaxy are significantly lacking.

Aims. In this study, we investigate the chemical enrichment of the SMC galaxy. In addition to the α and Fe-peak elements, we devote particular attention to the evolution of neutron-capture elements with a different origin; namely, r-process (Eu), weak s-process (Zr) and main s-process (Ba, La).

Methods. We developed chemical evolution models that use as their input the star formation histories obtained from colour-magnitude diagram fitting. We closely followed the chemical feedback provided by a large variety of nucleosynthetic sources. Our model predictions were compared with recent abundance measurements for the SMC.

Results. The developed framework aptly reproduces all the observables for elements up to the Fe-peak. The abundance patterns of n-capture elements are simultaneously reproduced only by assuming an enhanced contribution from the delayed r-process at low metallicity and a top-lighter IMF relative to the reference IMF by Kroupa 2001 (MNRAS, 322, 231). In this way, both the observed very high plateau in [Eu/Fe] and the rising trends in [s-process/Fe] ratios can be reproduced by the models.

Conclusions. This study provides, for the first time, information on the evolution of several n-capture elements in a massive dwarf irregular galaxy, also providing insight on several ingredients driving galactic evolution. Moreover, this work provides a test-bed for further modelling of the SMC in the context of the numerous surveys that will target the Magellanic Clouds in the next years.