宽吸收线类星体的综合研究：I。低电离度物体中HeI * 吸收线多重态的普遍性
A Comprehensive Study of Broad Absorption Line Quasars: I. Prevalence of HeI* Absorption Line Multiplets in Low-Ionization Objects
摘要：
中性氦多重谱HeI* 3189，3889，10830对类星体吸收气体的几何和物理条件是非常有用的诊断。到目前为止，只报告了少数HeI* 检测结果。使用一种新的方法，我们检测到HeI*3889吸收线在101个源的一个定义良好的样本285 MgII BAL类星体从SDSS DR 5选择。这使得HeI* BAL类星体的数量增加了一个数量级以上。我们进一步在样品中的50%（52/101）类星体中检测到HeI*3189。MgII BAL类星体中HeI* BALs的探测率总体上约为35%，并且随着光谱信噪比的增加而急剧增加，从信噪比<= 10时的18%增加到信噪比>= 35时的93%。这表明，如果光谱S/N足够高，大多数MgII LoBAL类星体都可以检测到HeI* BALs。这种令人惊讶的高HeI* BAL分数实际上是根据基于简单BAL模型的光电离计算预测的。结果表明，HeI* 吸收线可以用来寻找低z波段的BAL类星体，而这类星体通常是由地面光谱观测中常见的紫外吸收线所不能识别的。利用HeI*3889，我们从SDSS光谱数据库中发现了19个z<0.3的BAL类星体。HeI* BAL类星体的比例与LoBAL天体相似。
英文摘要：
Neutral Helium multiplets, HeI*3189,3889,10830 are very useful diagnostics to the geometry and physical conditions of the absorbing gas in quasars. So far only a handful of HeI* detections have been reported. Using a newly developed method, we detected HeI*3889 absorption line in 101 sources of a well-defined sample of 285 MgII BAL quasars selected from the SDSS DR5. This has increased the number of HeI* BAL quasars by more than one order of magnitude. We further detected HeI*3189 in 50% (52/101) quasars in the sample. The detection fraction of HeI* BALs in MgII BAL quasars is about 35% as a whole, and increases dramatically with increasing spectral signal-to-noise ratios, from 18% at S/N <= 10 to 93% at S/N >= 35. This suggests that HeI* BALs could be detected in most MgII LoBAL quasars, provided spectra S/N is high enough. Such a surprisingly high HeI* BAL fraction is actually predicted from photo-ionization calculations based on a simple BAL model. The result indicates that HeI* absorption lines can be used to search for BAL quasars at low-z, which cannot be identified by ground-based optical spectroscopic survey with commonly seen UV absorption lines. Using HeI*3889, we discovered 19 BAL quasars at z<0.3 from available SDSS spectral database. The fraction of HeI* BAL quasars is similar to that of LoBAL objects.
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