Density-weighted projections of the magnetic energy density between 3.25 Gyr and 5.6 Gyr, showing the evolution on scales of 250 kpc around the merger event (run A). The structure visible in the magnetic energy resembles the structure visible in the gas density. The galaxy cores have clearly merged after 4.4 Gyr. We indicate the region over which the field strength of the whole galaxy is averaged with circles (25 kpc), and also the region corresponding to an average over the center (5 kpc). The circles are centered on the density peak in the simulation.