H₂O(4−3) in 4C12.50. Left panel: ALMA image, collapsed in the indicated velocity range. The beam is shown with a shaded ellipse. The open ellipse corresponds to the area used for the extraction of the spectrum in the middle panel. Right panel: CO contours (levels: 2σ, 3σ and 5σ) over the Hubble Space Telescope [O III] image of Fig.1. Crosses are as in Fig. 1. The same applies to all following figures with similar layout.