The Pristine Dwarf-Galaxy survey - III. Revealing the nature of the Milky Way globular cluster Sagittarius II

Nicolas Longeard*, Nicolas Martin, Rodrigo Ibata, Else Starkenburg, Pascale Jablonka*, David S. Aguado, Raymond G. Carlberg, Patrick Côté, Jonay I. González Hernández, Romain Lucchesi, Khyati Malhan, Julio F. Navarro, Rubén Sánchez-Janssen, Guillaume F. Thomas, Kim Venn, Alan W. McConnachie

*Corresponding author for this work

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We present a new spectroscopic study of the faint Milky Way satellite Sagittarius II. Using multi-object spectroscopy from the Fibre LargeArray Multi Element Spectrograph, we supplement the dataset of Longeard et al. (2020) with 47 newly observed stars, 19 of which are identified as members of the satellite. These additional member stars are used toput tighter constraints on the dynamics and the metallicity properties of the system. We find a low velocity dispersion of SgrII v = 1.7 +/-0.5 km s-1, in agreement with the dispersion of Milky Way globular clusters of similar luminosity. We confirm the very metal-poor nature of the satellite ([Fe/H]_SgrII = -2.23 +/- 0.07) and find that the metallicity dispersion of Sgr II is not resolved, reaching only 0.20 atthe 95% confidence limit. No star with a metallicity below -2.5 is confidently detected. Therefore, despite the unusually large size of the system (rh = 35.5 +1.4-1.2 pc), we conclude that Sgr II is an old and metal-poor globular cluster of the Milky Way.
Original languageEnglish
Pages (from-to)2754-2762
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date5-Mar-2021
Publication statusPublished - May-2021


  • Astrophysics - Astrophysics of Galaxies

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