University of Leicester
Browse
aa9012-07.pdf (1.12 MB)

X-ray absorption in distant type II QSOs

Download (1.12 MB)
journal contribution
posted on 2012-10-24, 09:22 authored by M. Krumpe, G. Lamer, A. D. Schwope, A. Corral, F. J. Carrera, X. Barcons, M. Page, S. Mateos, Jonathan A. Tedds, M. G. Watson
Aims. We present the results of the X-ray spectral analysis of an XMM-Newton-selected type II QSO sample with z $\ge$ 0.5 and 0.5-10 keV flux of 0.3-33$\times$10-14 erg/s/cm2. The distribution of absorbing column densities in type II QSOs is investigated and the dependence of absorption on X-ray luminosity and redshift is studied. Methods. We inspected 51 spectroscopically classified type II QSO candidates from the XMM-Newton Marano field survey, the XMM-Newton-2dF wide angle survey (XWAS), and the AXIS survey to set-up a well-defined sample with secure optical type II identifications. Fourteen type II QSOs were classified and an X-ray spectral analysis performed. Since most of our sources have only ~40 X-ray counts (PN-detector), we carefully studied the fit results of the simulated X-ray spectra as a function of fit statistic and binning method. We determined that fitting the spectra with the Cash-statistic and a binning of minimum one count per bin recovers the input values of the simulated X-ray spectra best. Above 100 PN counts, the free fits of the spectrum's slope and absorbing hydrogen column density are reliable. Results. We find only moderate absorption ($N_{\rm H}$ = (2-10)$\times$1022 cm-2) and no obvious trends with redshift and intrinsic X-ray luminosity. In a few cases a Compton-thick absorber cannot be excluded. Two type II objects with no X-ray absorption were discovered. We find no evidence for an intrinsic separation between type II AGN and high X-ray luminosity type II QSO in terms of absorption. The stacked X-ray spectrum of our 14 type II QSOs shows no iron K$\alpha$ line. In contrast, the stack of the 8 type II AGN reveals a very prominent iron K$\alpha$ line at an energy of ~6.6 keV and an EW ~ 2 keV.

History

Citation

Astronomy & Astrophysics, 2008, 483 (2), pp. 415-424

Version

  • VoR (Version of Record)

Published in

Astronomy & Astrophysics

Publisher

EDP Sciences for European Southern Observatory (ESO)

issn

0004-6361

eissn

1432-0746

Copyright date

2008

Available date

2012-10-24

Publisher version

http://www.aanda.org/articles/aa/abs/2008/20/aa9012-07/aa9012-07.html

Language

en

Usage metrics

    University of Leicester Publications

    Categories

    Keywords

    Exports

    RefWorks
    BibTeX
    Ref. manager
    Endnote
    DataCite
    NLM
    DC