Protogalactic evolution and magnetic fields

We show that the relatively strong magnetic fields ($\ge 1 \mu$G) in high redshift objects can be explained by the combined action of an evolving protogalactic fluctuation and electrodynamic processes providing the magnetic seed fields. Three different seed field mechanisms are reviewed and incorporated into a spherical "top-hat" model and tidal torque theory for the fate of a forming galaxy in an expanding universe. Very weak fields $10^{-19} \sim 10^{-23}$G created in an expanding over-dense region are strongly enhanced due to the dissipative disk formation by a factor $\sim 10^4$, and subsequently amplified by strong non-axisymmetric flow by a factor $\sim 10^{6-10}$, depending on the cosmological parameters and the epoch of galaxy formation. The resulting field strength at $z \sim 0.395$ can be of the order of a few $\mu$G and be close to this value at $z \sim 2$.