(Barth et al. 2004). Because of their narrowness as well as the high S/N ratio of the SDSS spectrum, the doublet lines of both [\[S[II]{}\]]{} and [\[N[II]{}\]]{} are well isolated. [\[S[II]{}\]]{}, [\[N[II]{}\]]{}, and the narrow components of the Balmer lines have very similar full widths at half-maximum (FWHMs). We fit [\[S[II]{}\]]{} first, assuming that the doublet lines have the same width; a good fit is achieved with reduced ${\ensuremath{\chi^2}}=1.1$ (29 degrees of freedom) by using two Gaussians for each line. Then we fit the [H$\alpha$]{}–[\[N[II]{}\]]{} region, taking the best-fit model of [\[S[II]{}\]]{} as a template to model [\[N[II]{}\]]{} and narrow [H$\alpha$]{}. The line ratio of [\[N[II]{}\]]{} $\lambda$6583/$\lambda$6548 is set to the theoretical value 2.96, and their separation is fixed to the laboratory value. We use additional Gaussians to model the broad component of [H$\alpha$]{}, starting with one Gaussian and adding in more if the fit can be improved significantly according to the $F-$test. A good fit is achieved for broad [H$\alpha$]{} with just two Gaussians (Figure 1, right panel). As the broad [H$\beta$]{}  component is weak, we fit the total [H$\beta$]{} profile by assuming that its narrow component has the same profile as [\[S[II]{}\]]{} and that its broad component has 