Astrophys. J., Suppl. Ser., 217, 11 (2015/March-0)
A comprehensive study of broad absorption line quasars. I. Prevalence of HeI* absorption line multiplets in low-ionization objects.
LIU W.-J., ZHOU H., JI T., YUAN W., WANG T.-G., JIAN G., SHI X., ZHANG S., JIANG P., SHU X., WANG H., WANG S.-F., SUN L., YANG C., LIU B. and ZHAO W.
Abstract (from CDS):
Neutral helium multiplets, He i* λλ3189, 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*λ3889 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*λ3189 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 ≤ 10 to ∼93% at S/N ≥ 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 < 0.3 from the available SDSS spectral database. The fraction of He i* BAL quasars is similar to that of LoBAL objects.
galaxies: active - quasars: absorption lines - quasars: general
VizieR on-line data:
<Available at CDS (J/ApJS/217/11): table3.dat table4.dat table5.dat table6.dat tablea2.dat tablea3.dat tablea4.dat>
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