Journal Article

The environment of weak emission-line quasars

M. Nikołajuk and R. Walter

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 420, issue 3, pages 2518-2525
Published in print March 2012 | ISSN: 0035-8711
Published online February 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.20216.x
The environment of weak emission-line quasars

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The nature of weak emission-line quasars (WLQs) is probed by comparing the Baldwin effect (BEff) in WLQs and normal quasars [quasi-stellar objects (QSOs)]. We selected 81 high-redshift (z > 2.2) and two intermediate-redshift (z= 1.66 and 1.89) WLQs. Their rest-frame equivalent widths (EWs) of the C iv emission line and their Eddington ratio were obtained from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) quasar catalogue or from Diamond-Stanic et al. We compare the parameters of WLQs with those of 81 normal quasars from Bright Quasar Survey and 155 radio-quiet and radio-intermediate quasars detected by SDSS and Chandra. The influence of the Eddington ratio, LBol/LEdd, and the X-ray to optical luminosity ratio, αox, on the BEff is analysed. We find that WLQs follow a different relationship on the EW(C iv)–LBol/LEdd plane than normal quasars. This relationship disagrees with the super-Eddington hypothesis. The weakness/absence of emission lines in WLQs does not seem to be caused by their extremely soft ionizing continuum but by low covering factor (Ω/4π) of their broad-line region. Comparison of emission-line intensities indicates that the ratios of high-ionization line and low-ionization line regions (i.e. ΩHILLIL) are lower in WLQs than in normal QSOs. The covering factors of the regions producing C iv and Lyα emission lines are similar in both WLQs and QSOs.

Keywords: galaxies: active; quasars: emission lines; ultraviolet: galaxies; X-rays: galaxies

Journal Article.  5765 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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