Chandra observations of six QSOs at z ≈3

Takamitsu Miyaji, Günther Hasinger, Ingo Lehmann, Donald P. Schneider

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4 Scopus citations


We report the results of our Chandra observations of six QSOs at z ∼ 3 from the Palomer Transit Grism Survey. Our primary goal is to investigate the possible systematic change of α ox between z > 4 and z ∼ 3, between which a rapid rise of luminous QSO number density with cosmic time is observed. The summed spectrum showed a power-law spectrum with a photon index of F ≈ 1.9, which is similar to other unabsorbed active galactic nuclei. Combining our z ∼ 3 QSOs with X-ray observations of QSOs at z > 4 from literature or archives, we find a correlation of α ox with optical luminosity. This is consistent with the fact that the luminosity function slope of the luminous end of the X-ray-selected QSOs is steeper than that of optically selected QSOs. We discuss an upper limit to the redshift dependence of α ox using a Monte Carlo simulation. Within the current statistical errors, including the derived limits on the redshift dependence of α ox, we found that the behaviors of the X-ray and optically selected QSO number densities are consistent with each other.

Original languageEnglish (US)
Pages (from-to)659-665
Number of pages7
JournalAstronomical Journal
Issue number2
StatePublished - Feb 2006

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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