Variability of Low-ionization Broad Absorption-line Quasars Based on Multi-epoch Spectra from the Sloan Digital Sky Survey
Brandt, W. N.
Hall, P. B.
Grier, C. J.
Ak, N. Filiz
Schneider, D. P.
McGraw, S. M.
AffiliationUniv Arizona, Steward Observ
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PublisherIOP PUBLISHING LTD
CitationYi, W., Brandt, W. N., Hall, P. B., Vivek, M., Grier, C. J., Ak, N. F., ... & McGraw, S. M. (2019). Variability of Low-ionization Broad Absorption-line Quasars Based on Multi-epoch Spectra from the Sloan Digital Sky Survey. The Astrophysical Journal Supplement Series, 242(2), 28.
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AbstractWe present absorption variability results for 134 bona fide Mg II broad absorption-line (BAL) quasars at 0.46 less than or similar to z less than or similar to 2.3 covering days to similar to 10 yr in the rest frame. We use multiple-epoch spectra from the Sloan Digital Sky Survey, which has delivered the largest such BAL variability sample ever studied. Mg II-BAL identifications and related measurements are compiled and presented in a catalog. We find a remarkable time-dependent asymmetry in the equivalent width (EW) variation from the sample, such that weakening troughs outnumber strengthening troughs, the first report of such a phenomenon in BAL variability. Our investigations of the sample further reveal that (i) the frequency of BAL variability is significantly lower (typically by a factor of 2) than that in high-ionization BALQSO samples, (ii) Mg II-BAL absorbers tend to have relatively high optical depths and small covering factors along our line of sight, (iii) there is no significant EW-variability correlation between Mg II troughs at different velocities in the same quasar, and (iv) the EW-variability correlation between Mg II and Al III BALs is significantly stronger than that between Mg II and C IV BALs at the same velocities. These observational results can be explained by a combined transverse-motion/ionization-change scenario, where transverse motions likely dominate the strengthening BALs while ionization changes and/or other mechanisms dominate the weakening BALs.
VersionFinal published version
SponsorsChina Scholarships Council ; National Science Foundation of China [NSFC-11703076, U1631127]; West Light Foundation of the Chinese Academy of Sciences [Y6XB016001]; Chinese Academy of Sciences [U1631127]; Natural Sciences and Engineering Research Council of Canada (NSERC) [2017-05983]; National Research Council Canada; TUBITAK [115F037]; National Astronomical Observatories of China; Chinese Academy of Sciences (Strategic Priority Research Program, "The Emergence of Cosmological Structures") [XDB09000000]; Special Fund for Astronomy from the Ministry of Finance; Alfred P. Sloan Foundation; National Science Foundation; U.S. Department of Energy Office of Science; Center for High-Performance Computing at the University of Utah; CAS; People's Government of Yunnan Province; NSF [AST-1516784]