LOW-z Mg II BROAD ABSORPTION-LINE QUASARS FROM THE SLOAN DIGITAL SKY SURVEY

Journal Article · Sat May 01 04:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/714/1/367· OSTI ID:21448930

Shaohua, Zhang; Tingi, Wang; Huiyuan, Wang; Hongyan, Zhou; Xiaobo, Dong ^[1]

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1. Key Laboratory for Research in Galaxies and Cosmology, The University of Sciences and Technology of China, Chinese Academy of Sciences, Hefei, Anhui 230026 (China)

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{sup -1}, and (3) Mg II absorption-line width {Delta}v{sub c} {>=} 1600 km s{sup -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 {approx}90% of our sample are classical BAL quasars and the completeness is {approx}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 H{beta} 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.

• OSTI ID: 21448930
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 714; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
BLACK HOLES
COSMIC RADIO SOURCES
EMISSION
GALAXIES
IONIZATION
LINE WIDTHS
LUMINOSITY
MASS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
QUASARS
RED SHIFT
SORPTION