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Article Dans Une Revue The Astrophysical Journal Année : 2024

The Discovery of the Faintest Known Milky Way Satellite Using UNIONS

Simon E. T. Smith
  • Fonction : Auteur
William Cerny
  • Fonction : Auteur
Christian R. Hayes
  • Fonction : Auteur
Federico Sestito
  • Fonction : Auteur
Jaclyn Jensen
  • Fonction : Auteur
Alan W. Mcconnachie
  • Fonction : Auteur
Marla Geha
  • Fonction : Auteur
Julio F. Navarro
  • Fonction : Auteur
Ting S. Li
  • Fonction : Auteur
Ken Chambers
  • Fonction : Auteur
Stephen Gwyn
  • Fonction : Auteur
Michael J. Hudson
  • Fonction : Auteur
Eugene Magnier
  • Fonction : Auteur

Résumé

We present the discovery of Ursa Major III/UNIONS 1, the least luminous known satellite of the Milky Way, which is estimated to have an absolute V-band magnitude of $+{2.2}_{-0.3}^{+0.4}$ mag, equivalent to a total stellar mass of ${16}_{-5}^{+6}$ M . Ursa Major III/UNIONS 1 was uncovered in the deep, wide-field Ultraviolet Near Infrared Optical Northern Survey (UNIONS) and is consistent with an old (τ > 11 Gyr), metal-poor ([Fe/H] ~ -2.2) stellar population at a heliocentric distance of ~10 kpc. Despite its being compact (r h = 3 ± 1 pc) and composed of few stars, we confirm the reality of Ursa Major III/UNIONS 1 with Keck II/DEIMOS follow-up spectroscopy and identify 11 radial velocity members, eight of which have full astrometric data from Gaia and are co-moving based on their proper motions. Based on these 11 radial velocity members, we derive an intrinsic velocity dispersion of ${3.7}_{-1.0}^{+1.4}$ km s-1 but some caveats preclude this value from being interpreted as a direct indicator of the underlying gravitational potential at this time. Primarily, the exclusion of the largest velocity outlier from the member list drops the velocity dispersion to ${1.9}_{-1.1}^{+1.4}$ km s-1, and the subsequent removal of an additional outlier star produces an unresolved velocity dispersion. While the presence of binary stars may be inflating the measurement, the possibility of a significant velocity dispersion makes Ursa Major III/UNIONS 1 a high-priority candidate for multi-epoch spectroscopic follow-ups to deduce the true nature of this incredibly faint satellite.
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insu-04411638 , version 1 (25-01-2024)

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Simon E. T. Smith, William Cerny, Christian R. Hayes, Federico Sestito, Jaclyn Jensen, et al.. The Discovery of the Faintest Known Milky Way Satellite Using UNIONS. The Astrophysical Journal, 2024, 961, ⟨10.3847/1538-4357/ad0d9f⟩. ⟨insu-04411638⟩
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