Radial velocity of the surveyed stars as a function of the angular distance from the centre of the Sgr galaxy. Stars are colour-coded according to their iron abundance. The thick red line is the running median smoothed over 8′ radial bins, while the thin red lines mark the 16th and 84th percentiles of the RV distribution, with the same smoothing, approximately enclosing the ±1σ interval about the systemic velocity.