Mon. Not. R. Astron. Soc., 480, 2609-2627 (2018/October-3)
Pristine dwarf galaxy survey - I. A detailed photometric and spectroscopic study of the very metal-poor Draco II satellite.
LONGEARD N., MARTIN N., STARKENBURG E., IBATA R.A., COLLINS M.L.M., GEHA M., LAEVENS B.P.M., RICH R.M., AGUADO D.S., ARENTSEN A., CARLBERG R.G., COTE P., HILL V., JABLONKA P., GONZALEZ HERNANDEZ J.I., NAVARRO J.F., SANCHEZ-JANSSEN R., TOLSTOY E., VENN K.A. and YOUAKIM K.
Abstract (from CDS):
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 (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 the spectroscopic sample size compared to previous investigations, the velocity dispersion of the system 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+1.1–1.2 km s–1). We further show that the spectroscopically confirmed members of Dra II have a mean proper motion of (µα^*,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.
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
galaxies: dwarf - galaxies: individual: Draco II - Local Group
Table A1: [LMS2018] JDDD.dddddddd+DD.dddddddd N=51.
DES1 = DES J0034-4902 in Simbad.
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