The contribution of faint AGNs to the ionizing background at z ~ 4 A. Grazian, E. Giallongo, K. Boutsia, S. Cristiani, E. Vanzella, C. Scarlata, P. Santini, L. Pentericci, E. Merlin, N. Menci et al. (14 more) A&A, 613 (2018) A44 Published online: 30 May 2018 DOI: 10.1051/0004-6361/201732385