Intermediate-Width Emission Lines Of Active Galactic Nuclei

The dusty torus is the key element of the active galactic nuclei (AGNs). However, most investigations about the dusty torus are limited on the dust ther-mal emission, while the gas emission of the dusty torus is poorly understood. According to the unified model of AGNs, the dusty torus, which is exposed to the central ionizing source, can produce rich optical and ultraviolet (UV) emis-sion lines through photo-ionization processes. The widths of the emission lines (FWHM～2000 km s-1) are between the broad emission lines(BELs) and narrow emission lines(NELs). We call these emission lines as intermediate-width emis-sion lines (IELs). Basing on previous researches about IELs, we carry out series of work as follows.The main difficult of studying the IELs is the uncertainties of line-profile decompositions. With the aid of the principle of the coronagraph, we detected prominent UV IELs in a partially obscured quasar 01287, where the UV BELs are heavily suppressed by the dust extinction. Assuming that the IELR is virialized, we estimated its distance to the central black hole of～2.9 pc, which is similar to the inner radius of the dusty torus,～1.3 pc. Photo-ionization calculations suggest that the IELR has a hydrogen density of ～1088-1094 cm-3, within the range of values quoted for the dusty torus near the inner radius of the dusty torus. These results suggest that the IELR originates from the inner surface of the dusty torus. Analogues of 01287 could be found in a large number of partially obscured quasars. This indicates that the IELR may widely exist in quasars, and provide an observational foundation for further IEL studies.IELs provide a new avenue to investigate the gas physical properties in the dusty torus. We present a detailed analysis of a quasar SDSS J232444.80-094600.3 (SDSS J2324-0946), which is remarkable for its strong IELs with FWHM ≈2000 km s-1 shown in different emission lines:the permitted lines Lya λ1216,CⅣ A1549, semiforbidden line CⅢ] λ1909, and forbidden lines [OⅢ] λλ4959,5007. With the aid of photo-ionization model calculations, we found that the emission gas of the dusty torus has a hydrogen density of nH～1062-106.3 cm-3,a distance to the central ionizing source of ROELR～35-50 pc, a covering factor of CF 6%, and a dust-to-gas ratio of≤4% times of SMC. Such strong IELs, served as a useful diagnose,can provide an avenue to study the properties of gas in the dusty torus.With the HST and SDSS spectral data, we constructed a sample of type I AGNs with both the rest-frame UV and optical spectra. Through analysing this sample, we found that the distance of the IELR to the central black hole is statistically consistent with the inner radius of the dusty torus. This indicates that the inner face of the dusty torus is the main region of producing IELs. Basing on this relationship, we derived a formula of estimating black hole mass using IELs. Besides, IELs affect the black hole mass estimated using the BEL widths. The dispersion could be significantly reduced if the IELs are subtracted from the emission lines.