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Tracing the Early Milky Way with Globular Clusters: The Diagnostic Power of Neutron-Capture Elements

J. Schiappacasse-Ulloa, L. Berni, S. Lucatello, L. Magrini, A. Bragaglia, R. E. Giribaldi

Abstract

Globular clusters (GCs) are fundamental tracers of the early assembly of the Milky Way (MW). They formed in diverse environments -- including both our Galaxy and dwarf galaxies -- retaining chemical and dynamical signatures that encode their origins and the merger history of the Galaxy. Although significant progress has been made in characterising GC chemistry, most studies have focused on light, $α$-, and iron-peak elements. In contrast, neutron-capture (n-capture) elements remain sparsely investigated across the GC system, despite their unique ability to trace nucleosynthetic channels and star-formation timescales. A homogeneous and statistically robust mapping of n-process elements in a large sample of GCs would provide powerful constraints on their formation environments, chemical signatures of in situ and accreted systems, and refine our understanding of the early chemical evolution of the MW halo. Addressing this gap requires high-resolution, multiplexing, and blue-sensitive spectroscopy capable of accessing the full suite of n-capture diagnostics in several tens of stars per GC.

Tracing the Early Milky Way with Globular Clusters: The Diagnostic Power of Neutron-Capture Elements

Abstract

Globular clusters (GCs) are fundamental tracers of the early assembly of the Milky Way (MW). They formed in diverse environments -- including both our Galaxy and dwarf galaxies -- retaining chemical and dynamical signatures that encode their origins and the merger history of the Galaxy. Although significant progress has been made in characterising GC chemistry, most studies have focused on light, -, and iron-peak elements. In contrast, neutron-capture (n-capture) elements remain sparsely investigated across the GC system, despite their unique ability to trace nucleosynthetic channels and star-formation timescales. A homogeneous and statistically robust mapping of n-process elements in a large sample of GCs would provide powerful constraints on their formation environments, chemical signatures of in situ and accreted systems, and refine our understanding of the early chemical evolution of the MW halo. Addressing this gap requires high-resolution, multiplexing, and blue-sensitive spectroscopy capable of accessing the full suite of n-capture diagnostics in several tens of stars per GC.

Paper Structure

This paper contains 2 sections, 2 figures, 1 table.

Table of Contents

  1. Scientific Context
  2. A new facility beyond 2030

Figures (2)

  • Figure 1: [Eu/$\alpha$] ratio as a function of [Fe/H] for GCs of different origins. Monty2024 (left panel) and SchiappacasseUlloa2025 (right panel) show distinct chemical behaviours between in-situ (red symbols) and ex-situ clusters (blue and black symbols).
  • Figure 2: Example of a field of view populated with 2,000 high-resolution fibres. The two circles indicate areas of 2.5 and 5 deg$^2$, respectively. Small blue symbols mark fibre positions, while pink and purple dots denote stars.