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

AuthorsPage, M. J.; Carrera, Francisco J. CSIC ORCID CVN ; Stevens, J. A.; Ebrero, Jacobo CSIC ORCID; Blustin, A. J.
KeywordsGalaxies: active
Galaxies: evolution
Galaxies: formation
X-rays: galaxies
Issue DateOct-2011
PublisherOxford University Press
CitationMonthly Notices of the Royal Astronomical Society 416(4): 2792-2801 (2011)
AbstractThere exists a significant population of broad line, z∼ 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 C iv absorption lines in their ultraviolet spectra with equivalent width >5 Å. 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 ∼4 per cent, in agreement with recent estimates for the kinetic feedback from QSOs required to produce the M–σ 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.
Publisher version (URL)http://dx.doi.org/10.1111/j.1365-2966.2011.19226.x
Appears in Collections:(IFCA) Artículos
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