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Emission lines from the broad emission line region (BELR) and the narrowemission line region (NELR) of active galactic nuclei (AGNs) are extensivelystudied. However, between these two regions emission lines are rarely detected.We present a detailed analysis of a quasar SDSS J232444.80-094600.3 (SDSSJ2324$-$0946), which is remarkable for its strong intermediate-width emissionlines (IELs) with FWHM $\approx$ 1800 \kmps. The IEL component is presented indifferent emission lines, including the permitted lines \lya\ $\lambda$1216,\civ\ $\lambda$1549, semiforbidden line \ciii\ $\lambda$1909, and forbiddenlines \oiii\ $\lambda\lambda$4959, 5007. With the aid of photo-ionizationmodels, we found that the IELs are produced by gas with a hydrogen density of$n_{\rm H} \sim 10^{6.2}-10^{6.3}~\rm cm^{-3}$, a distance to the centralionizing source of $R \sim 35-50$ pc, a covering factor of CF $\sim$ 6\%, and adust-to-gas ratio of $\leq 4\%$ times of SMC. We suggest that the strong IELsof this quasar are produced by nearly dust-free and intermediate-density gaslocated at the skin of the dusty torus. Such strong IELs, served as a usefuldiagnose, can provide an avenue to study the properties of gas between the BELRand the NELR.

research in astronomy and astrophysics/research in astronomy and astrophysics

Strong Optical and UV Intermediate-Width Emission Lines in the Quasar  SDSS J232444.80-094600.3: Dust-Free and Intermediate-Density Gas at the Skin  of Dusty Torus ?