2025A&A...697A..19O

We address the chemical link between Terzan 5 (hereafter Ter5) and the Galactic bulge, as probed by the observed distributions of [α/Fe] abundance ratios with varying [Fe/H] and by suitable statistical tests to evaluate their significance. We also present a comprehensive review of the kinematic and evolutionary properties of Ter5, based on all the available observational signatures and the scenarios proposed so far in the literature for the formation and evolution of Ter5, as well as on the recent modelling of its star formation and chemical enrichment history. This analysis confirms the complex nature of this massive stellar system, with robust evidence of in situ bulge formation and of a subsequent evolution that cannot be simply explained by a single merging and/or accretion event of two globulars or a globular and a giant molecular cloud, as has been proposed in the literature, but it requires a more complex star formation likely accompanied by some self-enrichment.