The nature of X-ray-absorbed quasi-stellar objects
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AuthorPage, Mathew J.; Carrera Troyano, Francisco Jesús; Stevens, Jason A.; Ebrero Carrero, Jacobo; Blustin, Alexander J.
There 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 CIV absorption lines in their ultraviolet spectra
with equivalent width >5Å. 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 theM–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.
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