Speaker
Description
I will review the arguments in favour of/against a substantial
contribution of AGNs and/or star-forming galaxies to the reionization
of the Universe at z>5, by using extrapolations of the most recent
determination of the AGN and LBG high-z luminosity functions (LFs) and
their redshift evolution. A galaxy driven reionization requires a
significant contribution of faint dwarf galaxies and a LyC photon
escape fraction (f_esc) of the order of ~20 per cent, in tension with
observational constraints. I will then focus on the AGN contribution
to reionization. In particular, I will present a recent study based on
a sample of 1669 luminous QSOs from BOSS. Their f_esc distribution
shows a peak around zero and a long tail of higher values, with a
resulting mean f_esc~0.75 (independent of the QSO luminosity and/or
redshift). Combining this f_esc estimate with the observed evolution
of the AGN-LF, we compute the AGN contribution to the UV ionizing
background (UVB) as a function of redshift. AGN brighter than
one-tenth of the characteristic luminosity of the LF are able to
produce most of it up to z~3, whereas at higher redshifts, a
contribution of the galaxy population is required. Assuming an f_esc
for star-forming galaxies between 5.5 and 7.6 per cent, independent of
the galaxy luminosity and/or redshift, a remarkably good fit to the
observational UVB data up to z~6 is obtained.
| Affiliation | INAF-OATs |
|---|
