The chemical DNA of the Magellanic Clouds VI. Origin and evolution of neutron-capture elements in the SMC

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 strikingly lacking. Aims. In this study, we investigate the chemical enrichment of the SMC galaxy. Besides alpha and Fe-peak elements, we devote particular attention to the evolution of neutron-capture elements with different origin, namely r-process (Eu), weak s-process (Zr) and main s-process (Ba, La). Methods. We develop chemical evolution models that use as input the star formation histories obtained from colour-magnitude diagram fitting. We follow in detail the chemical feedback provided by a large variety of nucleosynthetic sources. Model predictions are compared with recent abundance measurements for the SMC. Results. The developed framework reproduces well 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). 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.

Figures (16)

• Figure 1: Global SFHs for the SMC galaxy as derived by Rubele18 and Massana22.
• Figure 2: Age-metallicity relation (top panel) and MDF (bottom panel) as predicted by the reference chemical evolution model adopting Rubele18 SFH (blue line, circles and histogram, respectively). The predicted age-metallicity relation is compared with the CMD-extracted relation by Rubele18, the thereotical curve by Pagel98, SMC GCs from low-resolution Parisi09Parisi15Parisi22Dias21 and high-resolution studies Mucciarelli23_GCs. Observed MDFs are from Mucciarelli23 and Hasselquist21.
• Figure 3: Age-metallicity relation (top panel) and MDF (bottom panel) as predicted by the reference chemical evolution model adopting Massana22 SFH (green curve, circles and histogram, respectively). Data as in Fig. \ref{['fig:AgeFeH_MDF_Rubele']}.
• Figure 4: [X/Fe] vs. [Fe/H] for light elements in the SMC. Abundance patterns are shown for Mg (left panel), Si (central panel) and Ni (right panel) for reference models adopting Rubele18 SFH (blue lines and cyan regions) and Massana22 SFH (green lines light-green regions). Solid lines are genuine chemical evolution tracks for models with a given SFH, whereas shaded regions are associated model predictions account for observational uncertainties ('synthetic model'). Data are from Mucciarelli23 and Mucciarelli23_GCs. Orange contour lines represent density lines of the observed stellar distributions in SMC field stars.
• Figure 5: [X/Fe] vs. [Fe/H] for n-capture elements in the SMC. Abundance patterns are shown for Eu (leftmost panel), Zr (second leftmost) and Ba (second rightmost) and La (rightmost). Solid lines are genuine chemical evolution tracks for the reference models adopting Rubele18 SFH (blue) and Massana22 SFH (green), whereas shaded cyan and light-green regions are associated model predictions account for observational uncertainties ('synthetic models'). Data are from Anoardo25 and Mucciarelli23 for SMC field stars (orange dots) and Mucciarelli23_GCs for SMC GCs (black dots). Orange contour lines represent density lines of the observed stellar distributions in SMC field stars.