【摘要】 斯隆数字巡天光谱数据中发现,类星体SDSS J2220+0109光谱中同时出现如下极为罕见的吸收线:氢巴尔末线Hα和Hβ,亚稳态He I* λλ3889、3189tt,CaⅡH、K,以及来自FeⅡ*能级的波数分别为7 955 cm^-1、13 474 cm^-1和13 673 cm^-1的众多吸收线.上述吸收线具有相似的速度结构,线宽达1 500 km·s^-1,相对于发射线表现出蓝移.研究结果表明,这些吸收线很可能来自部分电离区,密度n_E≈10⁶cm^-3,柱密度N_{H I}≈10²¹ cm^-2,Lyα共振散射对氢原子的激发起重要作用.SDSS J2220+0109斯隆r星等为16.56 mag,是探索活动星系核中特殊吸收线起源的理想实验室.将来的紫外光谱观测可以更加准确决定吸收气体的密度、柱密度、电离参数等物理性质;光学光谱监测有助于限定吸收线的产生机制.此外还发现,SDSS J2220+0109中的FeⅡ发射线显著区别于典型的窄线赛弗特Ⅰ型星系ⅠZw 1,很可能来自低密度气体,进一步研究有助于理解类星体中FeⅡ发射线的起源.更多还原

【Abstract】 We report the discovery of Balmer broad absorption lines（BALs） in the quasar SDSS J2220+0109 and present a detailed analysis of the peculiar absorption line spectra.The absorption lines are detected in HeⅠ^* multiplet at AA3189,3889 arising from the metastable helium 2³s level,and in Hαand Hβfrom the excited hydrogen H I n = 2 level,which are rarely seen in quasar spectra.There are also many absorption lines arising from excited FeⅡ^* levels 7955 cm^-1,13474 cm^-1 and 13673 cm^-1 in the wavelength range of 3100～3300 A.CaⅡH,K absorption line doublets are also clearly presented in its SDSS spectra.All absorption lines show a similar blueshifted velocity structure of△v≈—1500～0 km·s^-1 relative to the quasar systematic redshift determined from the emission lines.Detailed analysis suggests that the BALs should arise from partial ionized region with a column density of N_{H I}～10²¹ cm^-2 for an electron density of n_e≈10⁶ cm^-3;and the hydrogen n = 2 level be populated via collisional excitation with Lyαpumping. In addition to its peculiar absorption features,SDSS J2220+0109 also shows unusual FeⅡemission lines very likely originated from the low density gas of n_e≈10⁶ cm^-3,which is similar to that of the absorption gas.更多还原