Evolution of the magnetic energy (solid), thermal energy (dotted), and kinetic energy (dashed) for the simulation without star-formation (black) and with SN feedback (red). The initial magnetic field is in both cases B_IGM = 10^-5   μG, and the energies are computed in a small cube of 15 kpc size around the galaxy. The blue solid line is the magnetic energy for the magnetic seeding simulation (see Appendix).