Template comparison for the photoionizing source. Top panels: Rest-frame flux density of the AGN template (solid black lines), of black bodies with different temperatures T_* (dotted lines in the left-hand panel) and single stellar populations with different ages (dotted lines in the right-hand panel). The frequency threshold of photons responsible for the ionization of hydrogen, nitrogen, oxygen relevant to this study are marked for reference. Bottom panels: Ratio of O⁺ to N-ionizing photons produced by different templates, as a function of T_* (black bodies; left-hand panel) and burst age (right-hand panel). Empty circles refer to values integrated at any ν₀ > ν_ion, while filled circles refer to the “net” values (see Eq. (13)).