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 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+/-0.5Gyr) and metal poor. The CaHK photometry confirms the metal-poor nature of the satellite ([Fe/H]CaHK=-2.32+/-0.04dex) and suggests that Sgr II hosts more than one single stellar population ({sigma}[Fe/H]^CaHK^=0.11^+0.05^-0.03_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+/-0.05dex, {sigma}[Fe/H]^spectro^=0.10^+0.06^-0.04_dex). The velocity dispersion of the system is found to be {sigma}_v=2.7^+1.3^-1.0_km/s after excluding two potential binary stars. Sgr II's metallicity and absolute magnitude (M_V=-5.7+/-0.1mag) 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^+32.8^-23.0_M{sun}/L{sun}). Furthermore, using the Gaia Data Release 2, we constrain the orbit of the satellite and find an apocentre of 118.4^+28.4^-23.7_kpc and a pericentre 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.

Cone search capability for table J/MNRAS/491/356/table2 (Properties of our spectroscopic sample)

Cone search capability for table J/MNRAS/491/356/table3 (Velocities and individual metallicities for all stars observed more than once, per mask)