Journal Article

Intervening broad-line region clouds' effects on the optical/ultraviolet spectrum

Ye Wang, Gary J. Ferland, Chen Hu, Jian-Min Wang and Pu Du

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 424, issue 3, pages 2255-2264
Published in print August 2012 | ISSN: 0035-8711
Published online August 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21389.x
Intervening broad-line region clouds' effects on the optical/ultraviolet spectrum

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Abstract

Recent X-ray observations of Mrk 766 suggest that broad emission-line region clouds cross our line of sight and produce variable X-ray absorption. Here we investigate what optical/ultraviolet (UV) spectroscopic features would be produced by such ‘intervening broad-line region (BLR) clouds' (IBC) crossing our line of sight to the accretion disc, the source of the optical/UV continuum. Although the emission spectrum produced by intervening clouds is identical to the standard BLR model, they may produce absorption features on the optical or UV continuum. Single clouds will have little effect on the optical/UV spectrum because BLR clouds are likely to be much smaller than the accretion disc. This is unlike the X-ray case, where the radiation source is considerably smaller. However, an ensemble of intervening clouds will produce spectroscopic features in the far-ultraviolet including a strong depression between the Lyman limit and Lyα. The amount of the depression will indicate the line-of-sight covering factor of clouds, an unknown quantity that is important for the ionization of the intergalactic medium and the energy budget of active galactic nuclei (AGNs). Comparison with observations suggests that the Spectral Energy Distribution (SED) of Mrk 766 may be affected by IBC that may exist in most of AGNs.

Keywords: accretion, accretion discs; quasars: emission lines; quasars: general; galaxies: seyfert

Journal Article.  5021 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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