Broad absorption line disappearance and emergence using multiple-epoch spectroscopy from the Sloan Digital Sky Survey

S. M. McGraw, W. N. Brandt, C. J. Grier, N. Filiz Ak, P. B. Hall, D. P. Schneider, S. F. Anderson, P. J. Green, T. A. Hutchinson, C. L. Macleod, M. Vivek

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


We investigate broad absorption line (BAL) disappearance and emergence using a 470 BALquasar sample over ≤0.10-5.25 rest-frame years with at least three spectroscopic epochs for each quasar from the Sloan Digital Sky Survey. We identify 14 disappearing BALs over≤1.73-4.62 rest-frame years and 18 emerging BALs over ≤1.46-3.66 rest-frame years associated with the C IV λλ1548,1550 and/or Si IV λλ1393,1402 doublets, and report on their variability behaviour. BAL quasars in our data set exhibit disappearing/emerging C IV BALs at a rate of 2.3-0.7+0.9 and 3.0-0.8+1.0 per cent, respectively, and the frequency for BAL to non-BAL quasar transitions is 1.7-0.6+0.8 per cent. We detect four re-emerging BALs over ≤3.88 rest-frame years on average and three re-disappearing BALs over ≤4.15 rest-frame years on average, the first reported cases of these types. We infer BAL lifetimes along the line of sight to be nominally ≲100-1000 yr using disappearing C IV BALs in our sample. Interpretations of (re-)emerging and (re-)disappearing BALs reveal evidence that collectively supports both transverse-motion and ionization-change scenarios to explain BAL variations. We constrain a nominal C IV/Si IV BAL-outflow location of ≲100 pc from the central source and a radial size of ≳1× 10-7 pc (0.02 au) using the ionization-change scenario, and constrain a nominal outflow location of ≲0.5 pc and a transverse size of ~0.01 pc using the transverse-motion scenario. Our findings are consistent with previous work, and provide evidence in support of BALs tracing compact flow geometries with small filling factors.

Original languageEnglish (US)
Pages (from-to)3163-3184
Number of pages22
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Aug 11 2017
Externally publishedYes


  • Galaxies: active
  • Quasars: absorption lines
  • Quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Broad absorption line disappearance and emergence using multiple-epoch spectroscopy from the Sloan Digital Sky Survey'. Together they form a unique fingerprint.

Cite this