[O III]_88 μm/[N II]_122 μm luminosity ratio, computed with Cloudy, assuming n = 180 cm⁻³ and Z = Z_⊙, for the various templates adopted in our study: A black body radiation of various temperatures, T_*; an AGN as described in Eq. (14); and a single stellar population with different burst ages, based on Bruzual & Charlot (2003). The observed line ratio is marked with a light green shading. The observed line ratio is consistent with the expectations for a black body of T_* ≈ 25 000 K or with a single stellar population with age ≈9 Myr. The AGN template, as well as templates involving either hotter black body temperatures, or lower stellar population ages, appear to over-predict the [O III]/[N II] luminosity ratio.