Longeard, NicolasMartin, NicolasStarkenburg, ElseIbata, Rodrigo A.Collins, Michelle L. M.Laevens, Benjamin P. M.Mackey, DougalRich, R. MichaelAguado, David S.Arentsen, AnkeJablonka, PascaleHernandez, Jonay I. GonzalezNavarro, Julio F.Sanchez-Janssen, Ruben2020-03-032020-03-032020-03-032020-01-0110.1093/mnras/stz2854https://infoscience.epfl.ch/handle/20.500.14299/166911WOS:000512163600025We 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 and Keck II/DEIMOS multiobject spectroscopy. We derive and refine the Sgr II structural and stellar properties inferred at the time of its discovery. 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)([FeH]) = 0.11(-0.03)(+0.05) dex). Using the Ca infrared triplet measured from our highest signal-to-noise spectra, we confirm the metallicity and dispersion inferred from the Pristine photometric metallicities ([Fe/H](spectro) = -2.23 +/- 0.05 dex, sigma(spectro)([Fe/H]) = 0.10(-0.04)(+0.06) dex). The velocity dispersion of the system is found to be sigma(v) = 2.7(-1.0)(+1.3) km s(-1) after excluding two potential binary stars. Sgr II's metallicity and absolute magnitude (M-V = -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 (M/L = 23.0(-23.0)(+32.8) M-circle dot L-circle dot(-1)). Furthermore, using the Gaia Data Release 2, we constrain the orbit of the satellite and find an apocentre of 118.4(-23.7)(+28.4) kpc and a pericentre of 54.8(-6.1)(+3.3) 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.Astronomy & AstrophysicsAstronomy & Astrophysicsgalaxies: dwarflocal groupna-o anticorrelationglobular-clusterdark-matterhorizontal branchesdiscoverycatalogpopulationtelescopeevolutioncompaniontext::journal::journal article::research article