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A Comprehensive Study of Broad Absorption Line Quasars. I. Prevalence of HeI* Absorption Line Multiplets in Low-ionization Objects

【标题】A Comprehensive Study of Broad Absorption Line Quasars. I. Prevalence of HeI* Absorption Line Multiplets in Low-ionization Objects

【Title】

【DOI】10.1088/0067-0049/217/1/11

【作者】 Wen-Juan Liu; 周宏岩; 纪拓; Weimin Yuan; Ting-Gui Wang; Ge Jian; 史习珩; 张少华 ; 姜鹏; Xinwen Shu; Huiyuan Wang; Shu-Fen Wang; Luming Sun; Chenwei Yang; Bo Liu; Wen Zhao

【Author】 Wen-Juan Liu ; Zhou Hongyan ; Ji Tuo ; Weimin Yuan ; Ting-Gui Wang ; Ge Jian ; Shi Xiheng ; Zhang Shaohua ; Jiang Peng ; Xinwen Shu ; Huiyuan Wang ; Shu-Fen Wang ; Luming Sun ; Chenwei Yang ; Bo Liu ; Wen Zhao

【期刊】The Astrophysical Journal Supplement Series

【Journal】

【期刊年份】2015

【卷】217

【期】1

【关键词】 galaxies: active, quasars: absorption lines, quasars: general

【Keywords】 galaxies: active, quasars: absorption lines, quasars: general

【摘要】Neutral helium multiplets, He i* λ λ 3189,3889,10830, are very useful diagnostics for the geometry and physical conditions of the absorbing gas in quasars. So far only a handful of He i* detections have been reported. Using a newly developed method, we detected the He i*λ 3889 absorption line in 101 sources of a well-defined sample of 285 Mg ii broad absorption line (BAL) quasars selected from SDSS DR5. This has increased the number of He i* BAL quasars by more than one order of magnitude. We further detected He i*λ 3189 in 50% (52/101) of the quasars in the sample. The detection fraction of He i* BALs in Mg ii BAL quasars is ∼35% as a whole, and it increases dramatically with increasing spectral signal-to-noise ratio (S/N), from ∼18% at S/N ≤slant 10 to ∼93% at S/N ≥slant 35. This suggests that He i* BALs could be detected in most Mg ii LoBAL quasars, provided the spectra S/N is high enough. Such a surprisingly high He i* BAL fraction is actually predicted from photoionization calculations based on a simple BAL model. The result indicates that He i* absorption lines can be used to search for BAL quasars at low z, which cannot be identified by ground-based optical spectroscopic surveys with commonly seen UV absorption lines. Using He i* λ3889, we discovered 19 BAL quasars at z\lt 0.3 from the available SDSS spectral database. The fraction of He i* BAL quasars is similar to that of LoBAL objects.

【Abstract】Neutral helium multiplets, He i* λ λ 3189,3889,10830, are very useful diagnostics for the geometry and physical conditions of the absorbing gas in quasars. So far only a handful of He i* detections have been reported. Using a newly developed method, we detected the He i*λ 3889 absorption line in 101 sources of a well-defined sample of 285 Mg ii broad absorption line (BAL) quasars selected from SDSS DR5. This has increased the number of He i* BAL quasars by more than one order of magnitude. We further detected He i*λ 3189 in 50% (52/101) of the quasars in the sample. The detection fraction of He i* BALs in Mg ii BAL quasars is ∼35% as a whole, and it increases dramatically with increasing spectral signal-to-noise ratio (S/N), from ∼18% at S/N ≤slant 10 to ∼93% at S/N ≥slant 35. This suggests that He i* BALs could be detected in most Mg ii LoBAL quasars, provided the spectra S/N is high enough. Such a surprisingly high He i* BAL fraction is actually predicted from photoionization calculations based on a simple BAL model. The result indicates that He i* absorption lines can be used to search for BAL quasars at low z, which cannot be identified by ground-based optical spectroscopic surveys with commonly seen UV absorption lines. Using He i* λ3889, we discovered 19 BAL quasars at z\lt 0.3 from the available SDSS spectral database. The fraction of He i* BAL quasars is similar to that of LoBAL objects.

【基金/项目】 Natural Science Foundation of China grants (NSFC 11473025, 11033007, 11421303) ; the SOC program (CHINARE2012-02-03) ; National Basic Research Program of China (the 973 Program 2013CB834905)

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