6.2.1 Emission-line fluxes

Table 7 compares the flux intensities calculated by our models with those from the observations. The fluxes are given relative to H$\beta$, on a scale where H$\beta=100$. Most predicted line fluxes from each model are in fairly good agreement with the observed values and the two models produce very similar fluxes for most observed species. There are still some discrepancies in the few lines, e.g. $[$O II$]$ $\lambda \lambda$3726,3729 and $[$S II$]$ $\lambda \lambda$6716,6731. The discrepancies in $[$O II$]$ $\lambda \lambda$3726,3729 can be explained by either recombination contributions or intermediate phase caused by a complex density distribution (see e.g. discussion in Ercolano et al., 2003c). $[$S II$]$ $\lambda \lambda$6716,6731 was affected by shock-ionization and its true flux intensity is much lower without the shock fronts. Meanwhile, $[$Ar III$]$ 7751 was enhanced by the telluric line. The recombination line H$\delta$ $\lambda$4102 and He II $\lambda$5412 were also blended with the O II recombination lines. There are also some recombination contributions in the $[$O II$]$ $\lambda \lambda$7320,7330 doublet. Furthermore, the discrepancies in the faint auroral line [N II] $\lambda$5755 and [O III] $\lambda$4363 can be explained by the recombination excitation contribution (see section 3.3 in Liu et al., 2000).