Age map of the inner  ~300 kpc region of RX J1548.9+0851 (see Fig. 2). There is a clear segregation in age for the investigated faint galaxy population. Whilst younger objects are diffusely distributed and found mostly in the outskirts of the system, the oldest objects (>8 Gyr) form a clear elongated structure aligned with the orientation of the major axis of the central elliptical, indicated as solid line. Ellipses contain the same objects as those in Fig. 8. See text for details.