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    X-ray insights into the nature of PHL 1811 analogs and weak emission-line quasars: Unification with a geometrically thick accretion disk?

    251731.pdf (2.432Mb)
    Access Status
    Open access
    Authors
    Luo, B.
    Brandt, W.
    Hall, P.
    Wu, J.
    Anderson, S.
    Garmire, G.
    Gibson, R.
    Plotkin, Richard
    Richards, G.
    Schneider, D.
    Shemmer, O.
    Shen, Y.
    Date
    2015
    Type
    Journal Article
    
    Metadata
    Show full item record
    Citation
    Luo, B. and Brandt, W. and Hall, P. and Wu, J. and Anderson, S. and Garmire, G. and Gibson, R. et al. 2015. X-ray insights into the nature of PHL 1811 analogs and weak emission-line quasars: Unification with a geometrically thick accretion disk?. Astrophysical Journal. 805: 122.
    Source Title
    Astrophysical Journal
    DOI
    10.1088/0004-637X/805/2/122
    ISSN
    0004-637X
    School
    Department of Physics and Astronomy
    Remarks

    Copyright © 2015 The American Astronomical Society. All rights reserved

    URI
    http://hdl.handle.net/20.500.11937/51974
    Collection
    • Curtin Research Publications
    Abstract

    We present an X-ray and multiwavelength study of 33 weak emission-line quasars (WLQs) and 18 quasars that are analogs of the extreme WLQ, PHL 1811, at z ˜ 0.52.9. New Chandra 1.59.5 ks exploratory observations were obtained for 32 objects while the others have archival X-ray observations. Significant fractions of these luminous type 1 quasars are distinctly X-ray weak compared to typical quasars, including 16 (48%) of the WLQs and 17 (94%) of the PHL 1811 analogs with average X-ray weakness factors of 17 and 39, respectively. We measure a relatively hard ( 1.16 +0.32-0.37 ) effective power-law photon index for a stack of the X-ray weak subsample, suggesting X-ray absorption, and spectral analysis of one PHL 1811 analog, J1521+5202, also indicates significant intrinsic X-ray absorption. We compare composite Sloan Digital Sky Survey spectra for the X-ray weak and X-ray normal populations and find several opticalUV tracers of X-ray weakness, e.g., Fe II rest-frame equivalent width (REW) and relative color. We describe how orientation effects under our previously proposed shielding-gas scenario can likely unify the X-ray weak and X-ray normal populations. We suggest that the shielding gas may naturally be understood as a geometrically thick inner accretion disk that shields the broad line region from the ionizing continuum. If WLQs and PHL 1811 analogs have very high Eddington ratios, the inner disk could be significantly puffed up (e.g., a slim disk). Shielding of the broad emission-line region by a geometrically thick disk may have a significant role in setting the broad distributions of C IV REW and blueshift for quasars more generally.

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