BPT diagrams with the AGN photoionization models compared with the observations from the selected apertures in NGC 1068 (Fig. 1b). The BPT diagrams for [N II], [S II], and [O I] are shown on the left, middle, and right, respectively. The different shades of purple going from deep purple to pale lilac/white represent the ascending distance from the nucleus, as also noted with numbers, with “N” being the closest aperture. Also, from white to deep red, the different shades of red represent the range of ionization parameter values, −3.5 ≤ log U ≤ −1.5. All the models shown have solar abundances. The red diamonds represent the measured line ratios for the photoionization-dominated Seyfert 2 nucleus in NGC 1320. The Kewley, Kauffmann, and Schawinski lines correspond to the black, blue, and red solid lines, respectively. (a) ζ_CR = 10⁻¹⁴s⁻¹. (b) ζ_CR = 10⁻¹³s⁻¹. (c) ζ_CR = 10⁻¹²s⁻¹.