Top: Cloudy predictions for the He II/Hβ ratio as a function of the ionization parameter, U, and the gas density, n, for the cases of photoionization from star formation (SF, in green) and from AGN (in red). Photoionization from star formation yields He II/Hβ values < 0.1 in all the cases. Bottom: Map of the He II/Hβ line ratio in PJ308–21. Significance levels corresponding to S/N = 2, 4, 8, 16, 32 are shown in contours. Values as high as He II/Hβ >  0.5, as found in the quasar host, in the bridge, and in the outflow are strongly indicative of photoionization from AGN. Conversely, the two companions are consistent with photoionization from star formation.