部分遮蔽类星体SDSS J151653.22+190048.2的紫外波段中等宽度发射线起源

类星体SDSS J151653.22+190048.2 (简称J1516+1900)在紫外-光学-近红外波段展现出奇特的光谱性质:其光学Hα、Hβ和近红外的Paα、Paβ等发射线的半高全宽(full width at half maximum intensity, FWHM)均超过5000 km/s,等值宽度接近类星体平均值;而紫外波段光谱的常见发射线Lyβ、OVI、Lyα、NV、Si IV和CIV等,由FWHM1700 km/s的中等宽度成分主导.这种现象很可能是由于紫外发射线的宽线成分经尘埃消光,强度严重削弱,从而使得中等宽度成分凸显出来;在光学和近红外波段,尘埃消光减弱,发射线由宽线成分主导,潜在的中等宽度成分不容易被看到.根据中等宽度成分的线宽和J1516+1900中央超大质量黑洞的质量MBH5.75×108M⊙,在维里化假设下,估计中等宽度发射区到中央黑洞的距离约为1.6 pc.另一方面,利用J1516+1900丰富的观测谱线,结合光致电离模型计算,可以限定J1516+1900的中等宽度发射线区气体密度1012cm-3、电离参数10-0.65.据此估计该发射线区到中心黑洞距离0.016 pc,只有维里化距离的1%.这一矛盾结果预示着中等宽度发射区可能具有较为复杂的物理结构,未来需要观测更多类似J1516+1900的部分遮蔽类星体并进行系统的分类和研究.

Origin of Ultraviolet Intermediate-width Emission Lines in Partially Obscured Quasar SDSS J151653.22+190048.2

Quasar SDSS J151653.22+190048.2(J1516+1900) presents very peculiar spectral characters in the observed ultraviolet, optical, and infrared bands: the full widths at half maximum intensity(FWHM) of optical emission lines(Hα, Hβ, and infrared Paα and Paβ) are all larger than 5000 km/s, and the equivalent widths of these emission lines also approach to those of normal quasars;while the ultraviolet emission lines(Lyβ, OVI, Lyα, NV, Si IV, and CIV) are dominated by intermediate-width emission lines(IELs) with FWHM 1700 km/s. This phenomenon can be explained as a partially obscuration effect: the broad emission lines(BELs) in ultraviolet are heavily suppressed by the dust extinction and thus the IELs become prominent;the dust extinction in optical is not significant, and the IELs are hard to be detected due to the brightness of BELs. Using the IEL width and central super-massive black hole mass MBH 5.75 × 108 M⊙of J1516+1900, and assuming that the intermediate-width emission line region(IELR) is virialized, we estimate the distance of IEL region to central black hole is about 1.6 pc. On the other side, by combining the photo-ionization calculations and observed IELs intensity, we find the IELR has a density of 1012 cm-3,ionization parameter of 10-0.65, and its distance to the central region of 0.016 pc,which is one percent of that based on the virialized estimation. This contradiction can provide an important clue for studying the geometry, physical condition, and the origin of emission line region in active galactic nuclei.