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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

Globular cluster formation with multiple stellar populations: A comprehensive overview of a star-cloud interaction scenario

  • Kenji Bekki1
  • Madeleine McKenzie2
  1. 1ICRAR M468 The University of Western Australia 35 Stirling Hwy, Crawley Western Australia 6009 ,
  2. 2Observatories of the Carnegie Institution for Science , 813 Santa Barbara St., Pasadena, CA 91101 ,
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Abstract

We present a new scenario for globular cluster (GC) formation with multiple stellar populations, in which both the first and second populations (1P and 2P) form from growing giant molecular clouds (GMCs) polluted by surrounding asymptotic giant branch (AGB) stars. Unlike previous AGB-polluter scenarios, this star-cloud interaction framework alleviates the mass-budget and dilution-timing problems. Idealised analytic models reproduce the observed dependence of the 1P fraction and helium abundance spread on GC mass, and qualitatively reproduce the Na-O, C-N, and Mg-Al anticorrelations and Si-Al and Mg-isotope correlations. The Mg-K anticorrelation can be reproduced only if super-AGB stars contribute significantly to GMC enrichment. The weak dependence of Li abundances on [Na/Fe] and [Al/Fe] is reproduced when about 20% of the polluting AGB stars produce Li-rich ejecta, disfavouring models in which the polluters cannot produce Li. Iron-complex Type-II GCs can form through mergers of two GCs born from separate GMCs within a dwarf galaxy at different epochs. The scenario implies that young massive clusters formed at surface star-formation-rate densities well below 1M⊙ yr−1 kpc−2 are unlikely to develop multiple stellar populations, and predicts low 12C/13C ratios (≈5) in 2P stars, a [Na/Fe]-[F/Fe] anticorrelation, and P-rich stars with [P/Fe] >0.5 and [N/Fe]>0.5. We test these predictions against more than 30 observed properties of GCs with multiple stellar populations, representing one of the most comprehensive observational benchmarks against a specific GC formation scenario to date.

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Cite

BibTeXRIS
BibTeX
@article{bekki2026globular,
  title = {{Globular cluster formation with multiple stellar populations: A comprehensive overview of a star-cloud interaction scenario}},
  author = {Kenji Bekki and Madeleine McKenzie},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = oct,
  doi = {10.1093/mnras/stag1882},
  url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1882/8865310},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Globular cluster formation with multiple stellar populations: A comprehensive overview of a star-cloud interaction scenario
AU  - Kenji Bekki
AU  - Madeleine McKenzie
PY  - 2026
DA  - 2026/10/05
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag1882
UR  - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1882/8865310
AB  - We present a new scenario for globular cluster (GC) formation with multiple stellar populations, in which both the first and second populations (1P and 2P) form from growing giant molecular clouds (GMCs) polluted by surrounding asymptotic giant branch (AGB) stars. Unlike previous AGB-polluter scenarios, this star-cloud interaction framework alleviates the mass-budget and dilution-timing problems. Idealised analytic models reproduce the observed dependence of the 1P fraction and helium abundance spread on GC mass, and qualitatively reproduce the Na-O, C-N, and Mg-Al anticorrelations and Si-Al and Mg-isotope correlations. The Mg-K anticorrelation can be reproduced only if super-AGB stars contribute significantly to GMC enrichment. The weak dependence of Li abundances on [Na/Fe] and [Al/Fe] is reproduced when about 20% of the polluting AGB stars produce Li-rich ejecta, disfavouring models in which the polluters cannot produce Li. Iron-complex Type-II GCs can form through mergers of two GCs born from separate GMCs within a dwarf galaxy at different epochs. The scenario implies that young massive clusters formed at surface star-formation-rate densities well below 1M⊙ yr−1 kpc−2 are unlikely to develop multiple stellar populations, and predicts low 12C/13C ratios (≈5) in 2P stars, a [Na/Fe]-[F/Fe] anticorrelation, and P-rich stars with [P/Fe] >0.5 and [N/Fe]>0.5. We test these predictions against more than 30 observed properties of GCs with multiple stellar populations, representing one of the most comprehensive observational benchmarks against a specific GC formation scenario to date.
SN  - 0035-8711
SN  - 1365-2966
ER  -