Mean Energy Density of Photogenerated Magnetic Fields Throughout the
  Epoch of Reionization
  Magnetic fields are ubiquitous in the Universe. They seem to be present at
virtually all scales and all epochs. Yet, whether the fields on cosmological
scales are of astrophysical or cosmological origin remains an open major
problem. Here we focus on an astrophysical mechanism based on the
photoionization of the intergalactic medium during the Epoch of Reionization.
Building upon previous studies that depicted the physical mechanism around
isolated sources of ionization, we present here an analytic model to estimate
the level at which this mechanism contributed to the magnetization of the whole
Universe, thanks to the distribution of sources, before and alongside early
luminous structure formation. This model suggests that the Universe may be
globally magnetized to the order of, at least, a few $10^{-20}$~G comoving
(i.e. several $10^{-18}$~G during the Epoch of Reionization) by this mechanism,
prior to any amplification process.
