Magnetic field structure before the merger (at 3 Gyr) and after the merger (at 5 Gyr, i.e., about 0.6 Gyr after the merger of the core). Left: projection of the fluctuation of the toroidal magnetic field strength (local toroidal field minus mean toroidal field at the same radius) in the central 40 kpc. Right: radial profile of the toroidal magnetic field as a function of radius, including its rms distribution. Both plots refer to the reference run A.