N-emitters as possible signposts of globular cluster formation

¹ Observatoire de Genève, Université de Genève, Chemin Pegasi 51, 1290, Versoix, Switzerland
² CNRS, IRAP, 14 Avenue E. Belin, 31400, Toulouse, France
³ Institut d’Astrophysique de Paris, UMR 7095 CNRS, Sorbonne Université, 98bis, Bd Arago, 75014, Paris, France
⁴ University of Bologna, Department of Physics and Astronomy, Via Gobetti 93/2, 40129, Bologna, Italy
⁵ Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, 14-b Metrolohichna str., Kyiv 03143, Ukraine

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Received: 18 December 2025
Accepted: 23 February 2026

Abstract

Based on the unusual chemical abundance ratios of N-emitters, which resemble those of globular cluster (GC) stars, their compactness, high interstellar medium (ISM) densities, and other properties, it has been suggested that N-emitters could indicate the formation sites of globulars. A recent statistical study of the N-emitter population has quantified the frequency f_N of these rare objects and their redshift evolution (Morel et al. 2025, A&A, submitted, [arXiv:2511.20484]). Using these results, we tested whether N-emitters trace the formation of GCs and used the observed cosmic star formation rate density evolution to predict the cosmological evolution of the GC population with time, their age distribution, and the total present-day stellar mass density formed in globulars. The predicted age distribution of GCs strongly resembles the typical asymmetric observed distributions in the Galaxy and ellipiticals, with a peak at ∼11.5–12 Gyr and a longer tail extending to younger ages. We derive a total stellar mass density formed in N-emitters down to redshift zero of (2 − 4)×10⁵ M_⊙ Mpc⁻³, which matches within a factor of ∼2 the observed fraction of stellar mass found in the GC population at z = 0. These results provide additional indirect arguments supporting that N-emitters could represent signposts of a short phase of GC formation.