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

Longeard, Nicolas, Martin, Nicolas, Starkenburg, Else, Ibata, Rodrigo A, Collins, Michelle L. M., Geha, Marla, Laevens, Benjamin P M, Rich, R Michael, Aguado, David S, Arentsen, Anke , Carlberg, Raymond G, Côté, Patrick, Hill, Vanessa, Jablonka, Pascale, González Hernández, Jonay I, Navarro, Julio F, Sánchez-Janssen, Rubén, Tolstoy, Eline, Venn, Kim A and Youakim, Kris (2018) 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, 480 (2). pp. 2609-2627.

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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 < 5.9km 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,μδ) = (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.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
Longeard, Nicolas
Martin, Nicolas
Starkenburg, Else
Ibata, Rodrigo A
Collins, Michelle L.
Geha, Marla
Laevens, Benjamin P M
Rich, R Michael
Aguado, David S
Arentsen, Anke
Carlberg, Raymond G
Côté, Patrick
Hill, Vanessa
Jablonka, Pascale
González Hernández, Jonay I
Navarro, Julio F
Sánchez-Janssen, Rubén
Tolstoy, Eline
Venn, Kim A
Youakim, Kris
Date : 27 July 2018
DOI : 10.1093/mnras/sty1986
Copyright Disclaimer : This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords : galaxies: dwarf – galaxies: individual: Draco II – Local Group
Depositing User : Diane Maxfield
Date Deposited : 17 Sep 2019 12:29
Last Modified : 17 Sep 2019 12:29

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