Line-driven radiative outflows in luminous quasars

Rebecca A.A. Bowler, Paul C. Hewett, James T. Allen, Gary J. Ferland

Research output: Contribution to journalArticlepeer-review

37 Scopus citations


An analysis of ≃19 500 narrow (≲200 km s-1) CIV λλ1548.2,1550.8 absorbers in ≃34 000 Sloan Digital Sky Survey quasar spectra is presented. The statistics of the number of absorbers as a function of outflow velocity shows that in approximately two-thirds of outflows, with multiple C IV absorbers present, absorbers are line-locked at the 500 km s-1 velocity separation of the C IV absorber doublet; appearing as 'triplets' in the quasar spectra. Line-locking is an observational signature of radiative line-driving in outflowing material, where the successive shielding of 'clouds' of material in the outflow locks the clouds together in outflow velocity. Line-locked absorbers are seen in both broad absorption line (BAL) quasars and non-BAL quasars with comparable frequencies and with velocities out to at least 20 000 km s-1. There are no detectable differences in the absorber properties and the dust content of single C IV doublets and line-locked C IV doublets. The gas associated with both single and line-locked CIV absorption systems includes material with a wide range of ionization potential (14-138 eV). Both single and line-locked CIV absorber systems show strong systematic trends in their ionization as a function of outflow velocity, with ionization decreasing rapidly with increasing outflow velocity. Initial simulations, employing CLOUDY, demonstrate that a rich spectrum of line-locked signals at various velocities may be expected due to significant opacities from resonance lines of Li-, He- and H-like ions of O, C and N, along with contributions from He II and HI resonance lines. The simulations confirm that line-driving can be the dominant acceleration mechanism for clouds with N(H I) ≃ 1019 cm-2.

Original languageEnglish
Pages (from-to)359-377
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - Oct 8 2014

Bibliographical note

Publisher Copyright:
© 2014 The Authors.


  • Galaxies: active
  • Quasars: absorption lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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