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The Pristine Dwarf-Galaxy survey – II. In-depth observational study of the faint Milky Way satellite Sagittarius II

Longeard, Nicolas, Martin, Nicolas, Starkenburg, Else, Ibata, Rodrigo A, Collins, Michelle L M, Laevens, Benjamin P M, Mackey, Dougal, Rich, R Michael, Aguado, David S, Arentsen, Anke , Jablonka, Pascale, Hernández, Jonay I González, Navarro, Julio F and Sánchez-Janssen, Rubén (2019) The Pristine Dwarf-Galaxy survey – II. In-depth observational study of the faint Milky Way satellite Sagittarius II Monthly Notices of the Royal Astronomical Society.

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We present an extensive study of the Sagittarius II (Sgr II) stellar system using MegaCam g and i photometry, narrow-band, metallicity-sensitive Calcium H&K doublet photometry, augmented with Keck II/DEIMOS multi-object spectroscopy. We are able to derive and refine the Sgr II structural and stellar properties: the colour-magnitude diagram implies Sgr II is old (12.0 +- 0.5 Gyr) and metal-poor. The CaHK photometry confirms the metal-poor nature of the satellite ([Fe/H]CaHK = -2.32 +- 0.04 dex) and suggests that Sgr II hosts more than one single stellar population ({\sigma} CaHK = 0.11+0.05-0.03 dex). From the deep spectroscopic data, the velocity dispersion of the system is found to be {\sigma}vr = 2.7+1.3-1.0 km s-1 after excluding two potential binary stars. Using the Ca infrared triplet measured from our highest signal-to-noise spectra, we are able to confirm the metallicity and dispersion inferred from the Pristine photometric metallicities: ([Fe/H] = -2.23 +- 0.05 dex, {\sigma}spectro = 0.10+0.06-0.04 dex). Sgr II's metallicity and absolute magnitude (MV = -5.7 +- 0.1 mag) place the system on the luminosity-metallicity relation of the Milky Way dwarf galaxies despite its small size. The low, but resolved metallicity and velocity dispersions paint the picture of a slightly dark matter-dominated satellite. Furthermore, using the Gaia Data Release 2, we constrain the orbit of the satellite and find an apocenter of 118.4+28.4-23.7 kpc and a pericenter of 54.8+3.3-6.1 kpc. The orbit of Sgr II is consistent with the trailing arm of the Sgr stream and indicates that it is possibly a satellite of the Sgr dSph that was tidally stripped from the dwarf's influence.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
Longeard, Nicolas
Martin, Nicolas
Starkenburg, Else
Ibata, Rodrigo A
Collins, Michelle L
Laevens, Benjamin P M
Mackey, Dougal
Rich, R Michael
Aguado, David S
Arentsen, Anke
Jablonka, Pascale
Hernández, Jonay I González
Navarro, Julio F
Sánchez-Janssen, Rubén
Date : 12 October 2019
DOI : 10.1093/mnras/stz2854
Copyright Disclaimer : © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (
Uncontrolled Keywords : Galaxy: Dwarf, Local Group. Object: Sagittarius II, Sagittarius stream.
Depositing User : Clive Harris
Date Deposited : 06 Nov 2019 08:19
Last Modified : 06 Nov 2019 08:19

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