Ionized-gas emission flux. Left: Hα flux map. Right:[NII] flux map. Redder colours indicate a higher flux, with white (seen in the ring region) representing the highest flux. Contours are the same as in Fig. 3. One can note the stellar cluster inside the ring, 4′′ to the west (right) of the centre, most clearly seen in the Hα map, and also seen as a dip in the velocity dispersion in Fig. 5.