2010/04/02 by Shaohua Zhang, Tinggui Wang, Ting-Gui Wang +5 · 3 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Black hole (networking) #Emission spectrum #Equivalent width #Galaxies: Formation, Evolution, Phenomena #Galaxy #Gamma-ray bursts and supernovae #Physics #Quasar #Sky #Spectral line #astro-ph.CO
paper · pdf · doi:10.1088/0004-637x/714/1/367
40 pages, accepeted for publication in ApJ
arxiv created 2010/04/02 · openalex publication_date 2010/04/09 · arxiv updated 2015/05/18 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present a sample of 68 low- z Mg ii low-ionization broad absorption-line (loBAL) quasars. The sample is uniformly selected from the Sloan Digital Sky Survey Data Release 5 according to the following criteria: (1) redshift 0.4 < z ⩽ 0.8, (2) median spectral S/N>7 pixel −1 , and (3) Mg ii absorption-line width Δ v c ⩾ 1600 km s −1 . The last criterion is a trade-off between the completeness and consistency with respect to the canonical definition of BAL quasars that have the "balnicity index" BI>0 in C iv BAL. We adopted such a criterion to ensure that ∼90% of our sample are classical BAL quasars and the completeness is ∼80%, based on extensive tests using high- z quasar samples with measurements of both C iv and Mg ii BALs. We found (1) Mg ii BAL is more frequently detected in quasars with narrower Hβ emission line, weaker [O iii ] emission line, stronger optical Fe ii multiplets, and higher luminosity. In term of fundamental physical parameters of a black hole accretion system, loBAL fraction is significantly higher in quasars with a higher Eddington ratio than those with a lower Eddington ratio. The fraction is not dependent on the black hole mass in the range concerned. The overall fraction distribution is broad, suggesting a large range of covering factor of the absorption material. (2) [O iii ]-weak loBAL quasars averagely show undetected [Ne v ] emission line and a very small line ratio of [Ne v ] to [O iii ]. However, the line ratio in non-BAL quasars, which is much larger than that in [O iii ]-weak loBAL quasars, is independent of the strength of the [O iii ] line. (3) loBAL and non-loBAL quasars have similar colors in near-infrared to optical band but different colors in ultraviolet. (4) Quasars with Mg ii absorption lines of intermediate width are indistinguishable from the non-loBAL quasars in optical emission line properties but their colors are similar to loBAL quasars, redder than non-BAL quasars. We also discuss the implication of these results.