CRISTIANI, StefanoStefanoCRISTIANISerrano, Luisa MariaLuisa MariaSerranoFONTANOT, FabioFabioFONTANOTVANZELLA, ErosErosVANZELLAMonaco, PierluigiPierluigiMonaco2020-07-202020-07-2020160035-8711http://hdl.handle.net/20.500.12386/26515We use a sample of 1669 quasars (r < 20.15, 3.6 < z < 4.0) from the Baryon Oscillation Spectroscopic Survey to study the intrinsic shape of their continuum and the Lyman continuum photon escape fraction (f<SUB>esc,q</SUB>), estimated as the ratio between the observed flux and the expected intrinsic flux (corrected for the intergalactic medium absorption) in the wavelength range 865-885 Å rest frame. Modelling the intrinsic quasar (QSO) continuum shape with a power law, F<SUB>λ</SUB> ∝ λ<SUP>-γ</SUP>, we find a median γ = 1.30 (with a dispersion of 0.38, no dependence on the redshift and a mild intrinsic luminosity dependence) and a mean f<SUB>esc,q</SUB> = 0.75 (independent of the QSO luminosity and/or redshift). The f<SUB>esc,q</SUB> distribution shows a peak around zero and a long tail of higher values, with a resulting dispersion of 0.7. If we assume for the QSO continuum a double power-law shape (also compatible with the data) with a break located at λ<SUB>br</SUB> = 1000 Å and a softening ∆γ = 0.72 at wavelengths shorter than λ<SUB>br</SUB>, the mean f<SUB>esc,q</SUB> rises to 0.82. Combining our γ and f<SUB>esc,q</SUB> estimates with the observed evolution of the active galactic nucleus (AGN) luminosity function (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, if the present sample is representative of their properties. At higher redshifts, a contribution of the galaxy population is required. Assuming an escape fraction of Lyman continuum photons from 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. At lower redshift, the extrapolation of our empirical estimate agrees well with recent UVB observations, dispelling the so-called Photon Underproduction Crisis.STAMPAenArticle10.1093/mnras/stw18102-s2.0-84989203033000384676000014http://arxiv.org/abs/1603.09351v2https://academic.oup.com/mnras/article/462/3/2478/25895492016MNRAS.462.2478CFIS/05 - ASTRONOMIA E ASTROFISICA