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Article Dans Une Revue Monthly Notices of the Royal Astronomical Society Année : 2018

Pristine dwarf galaxy survey – I. A detailed photometric and spectroscopic study of the very metal-poor Draco II satellite

Nicolas Martin
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Else Starkenburg
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Rodrigo A. Ibata
Michelle L. M. Collins
  • Fonction : Auteur
Marla Geha
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Benjamin P. M. Laevens
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David S. Aguado
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Anke Arentsen
Raymond G. Carlberg
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Vanessa Hill
Jonay I. González Hernández
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Eline Tolstoy
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Kim Venn
Kris Youakim

Résumé

We present a detailed study of the faint Milky Way satellite Draco II (Dra II) from deep CFHT/MegaCam broad-band g and i photometry and narrow-band metallicity-sensitive CaHK observations, along with follow-up Keck II/DEIMOS multi-object spectroscopy. Forward modelling of the deep photometry allows us to refine the structural and photometric properties of Dra II: the distribution of stars in colour-magnitude space implies Dra II is old (13.5 ± 0.5 Gyr), very metal-poor, very faint (L_V = 180 ^{+124}_{-72} { L_⊙}), and at a distance d = 21.5 ± 0.4 { kpc}. The narrow-band, metallicity-sensitive CaHK Pristine photometry confirms this very low metallicity ([Fe/H] = -2.7 ± 0.1 dex). Even though our study benefits from a doubling of the spectroscopic sample size compared to previous investigations, the velocity dispersion of the system is still only marginally resolved (σ _{vr}< 5.9 { km s^{-1}} at the 95 per cent confidence level) and confirms that Dra II is a dynamically cold stellar system with a large recessional velocity (< vr> = -342.5^{+1.1}_{-1.2}{ km s^{-1}}). We further show that the spectroscopically confirmed members of Dra II have a mean proper motion of (μ _α ^*,μ _δ)=(1.26 ± 0.27,0.94 ± 0.28) { mas/yr} in the Gaia DR2 data, which translates to an orbit with a pericentre and an apocentre of 21.3 ^{+0.7}_{-1.0} and 153.8 ^{+56.7}_{-34.7} { kpc}, respectively. Taken altogether, these properties favour the scenario of Dra II being a potentially disrupting dwarf galaxy. The low-significance extra-tidal features we map around the satellite tentatively support this scenario.

Dates et versions

hal-02280824 , version 1 (06-09-2019)

Identifiants

Citer

Nicolas Longeard, Nicolas Martin, Else Starkenburg, Rodrigo A. Ibata, Michelle L. M. Collins, et al.. Pristine dwarf galaxy survey – I. A detailed photometric and spectroscopic study of the very metal-poor Draco II satellite. Monthly Notices of the Royal Astronomical Society, 2018, 480 (2), pp.2609-2627. ⟨10.1093/mnras/sty1986⟩. ⟨hal-02280824⟩
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