The role of AGN jets in the reionization epoch
  The reionization of the Universe ends the dark ages that started after the
recombination era. In the case of H, reionization finishes around $z\sim 6$.
Faint star-forming galaxies are the best candidate sources of the H-ionizing
radiation, although active galactic nuclei may have also contributed. We have
explored whether the termination regions of the jets from active galactic
nuclei may have contributed significantly to the ionization of H in the late
reionization epoch, around $z\sim 6-7$. We assumed that, as it has been
proposed, active galactic nuclei at $z\sim 6$ may have presented a high jet
fraction, accretion rate, and duty cycle, and that non-thermal electrons
contribute significantly to the pressure of jet termination regions. Empirical
black-hole mass functions were adopted to characterize the population of active
galactic nuclei. From all this, estimates were derived for the isotropic
H-ionizing radiation produced in the jet termination regions, at $z\sim 6$,
through inverse Compton scattering off CMB photons. We find that the
termination regions of the jets of active galactic nuclei may have radiated
most of their energy in the form of H-ionizing radiation at $z\sim 6$. For
typical black-hole mass functions at that redshift, under the considered
conditions (long-lasting, common, and very active galactic nuclei with jets),
the contribution of these jets to maintain (and possibly enhance) the
ionization of H may have been non-negligible. We conclude that the termination
regions of jets from active galactic nuclei could have had a significant role
in the reionization of the Universe at $z\gtrsim 6$.
