higher ($7.6 \times 10^{40}$ [erg s$^{-1}$]{}), and the luminosity of [\[O[III]{}\]]{}$\lambda5007$ is $1.1 \times 10^{41}$ [erg s$^{-1}$]{}.

To test the reliability of the broad components of Balmer lines, we refit the [H$\alpha$]{}–[\[N[II]{}\]]{} complex and [H$\beta$]{} using as a template for each line the [\[O[III]{}\]]{}$\lambda 5007$ profile derived from its double-Gaussian model. The results are totally unacceptable; the reduced ${\ensuremath{\chi^2}}= 12$ and 37, respectively, for the [H$\beta$]{} and the [H$\alpha$]{}–[\[N[II]{}\]]{} complex, with obvious large residuals. This is evident by directly comparing the profiles of [H$\beta$]{} and [\[O[III]{}\]]{}$\lambda5007$, as shown in the inset of Figure 1 (with [\[O[III]{}\]]{}$\lambda 5007$ scaled to have the same peak flux density as [H$\beta$]{}); [H$\beta$]{} has an additional much broader, albeit low-contrast ($f_{\lambda} 
\lesssim 8 \times 10^{-17}$ [erg s$^{-1}$ cm$^{-2}$ Å$^{-1}$]{}), component that is not present in [\[O[III]{}\]]{}$\lambda 5007$. Also evident in the inset is that [\[O[III]{}\]]{} is slightly broader than [H$\beta$]{}  \[by $\sim120$ [$\mathrm{km~s^{-1}}$]{}, in height range $f_{\lambda} \approx (10-20) \times 
10^{-17}$ [erg s$^{-1}$ cm$^{-2}$ Å$^{-1}$]{}\]. We also tried another fitting scheme in which we model the narrow Balmer lines with the total profile of [\[O[III]{}\]]{}$\lambda 5007$ and the broad component of the Balmer lines with two Gaussians; the fitting results are also unacceptable, with reduced 