  Magnetic fields play a very important role in the evolution of galaxies
through their direct impact on star formation and stellar feedback-induced
turbulence. However, their co-evolution with these processes has still not been
thoroughly investigated, and the possible effect of the initial conditions is
largely unknown. This letter presents the first results from a series of
high-resolution numerical models, aimed at deciphering the effect of the
initial conditions and of stellar feedback on the evolution of the galactic
magnetic field in isolated, Milky-Way-like galaxies. The models start with an
ordered, either poloidal or toroidal, magnetic field of varying strength, and
are evolved with and without supernova feedback. They include a dark matter
halo, a stellar and a gaseous disk, as well as the appropriate cooling and
heating processes for the interstellar medium. Independently of the initial
conditions, the galaxies develop a turbulent velocity field and a random
magnetic field component in under 15 Myrs. Supernova feedback is extremely
efficient in building a random magnetic field component up to large galactic
heights. However, a random magnetic field emerges even in runs without
feedback, which points to an inherent instability of the ordered component.
Supernova feedback greatly affects the velocity field of the galaxy up to large
galactic heights, and helps restructure the magnetic field up to 10 kpc above
the disk, independently of the initial magnetic field morphology. On the other
hand, the initial morphology of the magnetic field can accelerate the
development of a random component at large heights. These effects have
important implications for the study of the magnetic field evolution in galaxy
simulations.
