BPT diagrams as shown in Fig. 10, here in comparison with the photoionization grids obtained from the 3MdB database using CLOUDY models. The top and bottom panels show the model results for Z = 0.0076 and Z = 0.019, respectively. For comparison, the sample median metallicity is Z = 0.0086. Blue lines represent different stellar ages of 1, 3, 4, 5.6, and 8.9 × 10⁶ years as ionization sources and are roughly oriented from top right to bottom left as age increases, although not linearly. Red lines represent variation in the photoionization parameter, ranging from log(U) between −4.0 and −2.0 (in steps of 0.5), roughly oriented from top left to bottom right as U decreases. Some stellar age values are displayed in the top-left panel, along with the increasing U orientation.