TY - JOUR
T1 - Pristine dwarf galaxy survey - I. A detailed photometric and spectroscopic study of the very metal-poor Draco II satellite
AU - Longeard, Nicolas
AU - Martin, Nicolas
AU - Starkenburg, Else
AU - Ibata, Rodrigo A.
AU - Collins, Michelle L.M.
AU - Geha, Marla
AU - Laevens, Benjamin P. M.
AU - Rich, R. Michael
AU - Aguado, David S.
AU - Arentsen, Anke
AU - Carlberg, Raymond G.
AU - Côté, Patrick
AU - Hill, Vanessa
AU - Jablonka, Pascale
AU - González Hernández, Jonay I.
AU - Navarro, Julio F.
AU - Sánchez-Janssen, Rubén
AU - Tolstoy, Eline
AU - Venn, Kim A.
AU - Youakim, Kris
PY - 2018/10
Y1 - 2018/10
N2 - We present a detailed study of the faint Milky Way satellite Draco II (Dra II) from deepCFHT/MegaCam broad-band g and i photometry and narrow-band metallicity-sensitive CaHKobservations, 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 (LV = 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 thespectroscopic sample size compared to previous investigations, the velocity dispersion of thesystem is still only marginally resolved (σvr < 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⟩ =−342.5−1.2+1.1 km s−1). We further show that the spectroscopically confirmed membersof Dra II have a mean proper motion of (μ∗α,μδ ) = (1.26 ± 0.27, 0.94 ± 0.28) mas/yr in theGaia DR2 data, which translates to an orbit with a pericentre and an apocentre of 21.3−1.0+0.7 and 153.8−34.7+56.7 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.
AB - We present a detailed study of the faint Milky Way satellite Draco II (Dra II) from deepCFHT/MegaCam broad-band g and i photometry and narrow-band metallicity-sensitive CaHKobservations, 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 (LV = 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 thespectroscopic sample size compared to previous investigations, the velocity dispersion of thesystem is still only marginally resolved (σvr < 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⟩ =−342.5−1.2+1.1 km s−1). We further show that the spectroscopically confirmed membersof Dra II have a mean proper motion of (μ∗α,μδ ) = (1.26 ± 0.27, 0.94 ± 0.28) mas/yr in theGaia DR2 data, which translates to an orbit with a pericentre and an apocentre of 21.3−1.0+0.7 and 153.8−34.7+56.7 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.
KW - galaxies: dwarf, galaxies: individual: Draco II, Local Group, Astrophysics - Astrophysics of Galaxies
U2 - 10.1093/mnras/sty1986
DO - 10.1093/mnras/sty1986
M3 - Article
SN - 0035-8711
VL - 480
SP - 2609
EP - 2627
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -