The nature of X-ray-absorbed quasi-stellar objects

M. J. Page, F. J. Carrera, J. A. Stevens, J. Ebrero, A. J. Blustin

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There exists a significant population of broad line, z similar to 2 quasi-stellar objects ( QSOs) which have heavily absorbed X-ray spectra. Follow-up observations in the submillimetre show that these QSOs are embedded in ultraluminous starburst galaxies, unlike most unabsorbed QSOs at the same redshifts and luminosities. Here we present X-ray spectra from XMM-Newton for a sample of five such X-ray-absorbed QSOs that have been detected at submillimetre wavelengths. We also present spectra in the rest-frame ultraviolet from ground-based telescopes. All the five QSOs are found to exhibit strong CIV absorption lines in their ultraviolet spectra with equivalent width >5 angstrom. The X-ray spectra are inconsistent with the hypothesis that these objects show normal QSO continua absorbed by low-ionization gas. Instead, the spectra can be modelled successfully with ionized absorbers, or with cold absorbers if they possess unusually flat X-ray continuum shapes and unusual optical to X-ray spectral energy distributions. We show that the ionized absorber model provides the simplest, most self-consistent explanation for their observed properties. We estimate that the fraction of radiated power that is converted into kinetic luminosity of the outflowing winds is typically similar to 4 per cent, in agreement with recent estimates for the kinetic feedback from QSOs required to produce the M-sigma relation, and consistent with the hypothesis that the X-ray-absorbed QSOs represent the transition phase between obscured accretion and the luminous QSO phase in the evolution of massive galaxies.

Original languageEnglish
Pages (from-to)2792-2801
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - Oct 2011


  • galaxies: active
  • galaxies: evolution
  • galaxies: formation
  • X-rays: galaxies


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