AGN jets versus accretion as reionization sources
  Cosmic reionization put an end to the dark ages that came after the
recombination era. Observations seem to favor the scenario where massive stars
generating photons in low-mass galaxies were responsible for the bulk of
reionization. Even though a possible contribution from accretion disks of
active galactic nuclei (AGN) has been widely considered, they are currently
thought to have had a minor role in reionization. Our aim is to study the
possibility that AGN contributed to reionization not only through their
accretion disks, but also through ionizing photons coming from the AGN jets
interacting with the IGM. We adopt an empirically derived AGN luminosity
function at $z\simeq6$, use X-ray observations to correct it for the presence
of obscured sources, and estimate the density of jetted AGN. We then use
analytical calculations to derive the fraction of jet energy that goes into
ionizing photons. Finally, we compute the contribution of AGN jets to the H II
volume filling factor at redshifts $z\simeq15-5$. We show that the contribution
of the AGN jet lobes to the reionization of the Universe at $z\sim6$ might have
been as high as $\gtrsim 10$\% of that of star-forming galaxies, under the most
favorable conditions of jetted and obscuration fraction. The contribution of
AGN to the reionization, while most likely not dominant, could have been higher
than previously assumed, thanks to the radiation originated in the jet lobes.
