A stellar stream remnant of a globular cluster below the metallicity floor

Nicolas F. Martin (), Kim A. Venn, David S. Aguado, Else Starkenburg, Jonay I. González Hernández, Rodrigo A. Ibata, Piercarlo Bonifacio, Elisabetta Caffau, Federico Sestito, Anke Arentsen, Carlos Allende Prieto, Raymond G. Carlberg, Sébastien Fabbro, Morgan Fouesneau, Vanessa Hill, Pascale Jablonka, Georges Kordopatis, Carmela Lardo, Khyati Malhan, Lyudmila I. Mashonkina, Alan W. McConnachie, Julio F. Navarro, Rubén Sánchez-Janssen, Guillaume F. Thomas, Zhen Yuan and Alessio Mucciarelli
Additional contact information
Nicolas F. Martin: Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg
Kim A. Venn: University of Victoria
David S. Aguado: University of Cambridge
Else Starkenburg: University of Groningen
Jonay I. González Hernández: Instituto de Astrofísica de Canarias
Rodrigo A. Ibata: Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg
Piercarlo Bonifacio: GEPI, Observatoire de Paris, Université PSL, CNRS
Elisabetta Caffau: GEPI, Observatoire de Paris, Université PSL, CNRS
Federico Sestito: University of Victoria
Anke Arentsen: Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg
Carlos Allende Prieto: Instituto de Astrofísica de Canarias
Raymond G. Carlberg: University of Toronto
Sébastien Fabbro: University of Victoria
Morgan Fouesneau: Max-Planck-Institut für Astronomie
Vanessa Hill: Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange
Pascale Jablonka: GEPI, Observatoire de Paris, Université PSL, CNRS
Georges Kordopatis: Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange
Carmela Lardo: Università di Bologna
Khyati Malhan: Stockholm University
Lyudmila I. Mashonkina: Russian Academy of Sciences
Alan W. McConnachie: NRC Herzberg Astronomy & Astrophysics
Julio F. Navarro: University of Victoria
Rubén Sánchez-Janssen: UK Astronomy Technology Centre, Royal Observatory
Guillaume F. Thomas: Instituto de Astrofísica de Canarias
Zhen Yuan: Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg
Alessio Mucciarelli: Università di Bologna

Nature, 2022, vol. 601, issue 7891, 45-48

Abstract: Abstract Stellar ejecta gradually enrich the gas out of which subsequent stars form, making the least chemically enriched stellar systems direct fossils of structures formed in the early Universe1. Although a few hundred stars with metal content below 1,000th of the solar iron content are known in the Galaxy2–4, none of them inhabit globular clusters, some of the oldest known stellar structures. These show metal content of at least approximately 0.2% of the solar metallicity $$([{\rm{Fe}}/{\rm{H}}]\gtrsim -2.7)$$ ( [ Fe / H ] ≳ − 2.7 ) . This metallicity floor appears universal5,6, and it has been proposed that protogalaxies that merged into the galaxies we observe today were simply not massive enough to form clusters that survived to the present day7. Here we report observations of a stellar stream, C-19, whose metallicity is less than 0.05% of the solar metallicity $$([{\rm{F}}{\rm{e}}/{\rm{H}}]=-3.38\pm 0.06\,({\rm{s}}{\rm{t}}{\rm{a}}{\rm{t}}{\rm{i}}{\rm{s}}{\rm{t}}{\rm{i}}{\rm{c}}{\rm{a}}{\rm{l}})\pm 0.20\,({\rm{s}}{\rm{y}}{\rm{s}}{\rm{t}}{\rm{e}}{\rm{m}}{\rm{a}}{\rm{t}}{\rm{i}}{\rm{c}}))$$ ( [ F e / H ] = − 3.38 ± 0.06 ( s t a t i s t i c a l ) ± 0.20 ( s y s t e m a t i c ) ) . The low metallicity dispersion and the chemical abundances of the C-19 stars show that this stream is the tidal remnant of the most metal-poor globular cluster ever discovered, and is significantly below the purported metallicity floor: clusters with significantly lower metallicities than observed today existed in the past and contributed their stars to the Milky Way halo.

Date: 2022
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DOI: 10.1038/s41586-021-04162-2

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