EDGE: the puzzling ellipticity of Eridanus II’s star cluster and its implications for dark matter at the heart of an ultra-faint dwarf - Archive ouverte HAL
Article Dans Une Revue Mon.Not.Roy.Astron.Soc. Année : 2022

EDGE: the puzzling ellipticity of Eridanus II’s star cluster and its implications for dark matter at the heart of an ultra-faint dwarf

Matthew D.A. Orkney
  • Fonction : Auteur
Justin I. Read
  • Fonction : Auteur
Oscar Agertz
  • Fonction : Auteur
Andrew Pontzen
  • Fonction : Auteur
Martin P. Rey
  • Fonction : Auteur
Alex Goater
  • Fonction : Auteur
Ethan Taylor
  • Fonction : Auteur
Stacy Y. Kim
  • Fonction : Auteur

Résumé

The Eridanus II (EriII) ‘ultra-faint’ dwarf has a large (15 pc) and low-mass (4.3 × 10^3 M_⊙) star cluster (SC) offset from its centre by 23 ± 3 pc in projection. Its size and offset are naturally explained if EriII has a central dark matter core, but such a core may be challenging to explain in a ΛCDM cosmology. In this paper, we revisit the survival and evolution of EriII’s SC, focusing for the first time on its puzzlingly large ellipticity (⁠|$0.31^{+0.05}_{-0.06}$|⁠). We perform a suite of 960 direct N-body simulations of SCs, orbiting within a range of spherical background potentials fit to ultra-faint dwarf (UFD) galaxy simulations. We find only two scenarios that come close to explaining EriII’s SC. In the first scenario, EriII has a low-density dark matter core (of size |${\sim}70\, \text{pc}$| and density |$\lesssim 2\times 10^8\, \text{M}_{\odot }\, \text{kpc}^{-3}$|⁠). In this model, the high ellipticity of EriII’s SC is set at birth, with the lack of tidal forces in the core allowing its ellipticity to remain frozen for long times. In the second scenario, EriII’s SC orbits in a partial core, with its high ellipticity owing to its imminent tidal destruction. However, this latter model struggles to reproduce the large size of EriII’s SC, and it predicts substantial tidal tails around EriII’s SC that should have already been seen in the data. This leads us to favour the cored model. We discuss potential caveats to these findings, and the implications of the cored model for galaxy formation and the nature of dark matter.
Fichier principal
Vignette du fichier
stac1755.pdf (4.07 Mo) Télécharger le fichier
Origine Fichiers éditeurs autorisés sur une archive ouverte

Dates et versions

hal-03577512 , version 1 (11-04-2023)

Identifiants

Citer

Matthew D.A. Orkney, Justin I. Read, Oscar Agertz, Andrew Pontzen, Martin P. Rey, et al.. EDGE: the puzzling ellipticity of Eridanus II’s star cluster and its implications for dark matter at the heart of an ultra-faint dwarf. Mon.Not.Roy.Astron.Soc., 2022, 515 (1), pp.185-200. ⟨10.1093/mnras/stac1755⟩. ⟨hal-03577512⟩
39 Consultations
39 Téléchargements

Altmetric

Partager

More