Chandra Observations of Six QSOs at z $\approx$ 3

Abstract

We report the results of our Chandra observations of six QSOs at $z\sim 3$ from the Palomer Transit Grism Survey. Our primary goal is to investigate the possible systematic change of ${\alpha }_{ox}$ between $z>4$ and $z\sim 3$, between which a rapid rise of luminous QSO number density with cosmic time is observed. The summed spectrum showed a power-law spectrum with photon index of $\Gamma \approx 1.9$, which is similar to other unabsorbed AGNs. Combining our $z\sim 3$ QSOs with X-ray observations of QSOs at $z>4$ from literaure/archive, we find a correlation of ${\alpha }_{\mathrm{ox}}$ 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 ${\alpha }_{ox}$ using a Monte-Carlo simulation. Within the current statistical errors including the derived limits on the redshift dependence of ${\alpha }_{\mathrm{ox}}$, we found that the behaviors of the X-ray and optically-selected QSO number densities are consistent with each other.

arXiv comment13 Pages, 3 Figures, Astronomical Journal in press, An entry in Table 2 corrected--Log Lx for PC 1000+4751 from 44.0 (incorrect) to 45.0 (correct). A few minor errors corrected

References in corpus (17)

• The Sloan Digital Sky Survey: Technical Summary
• Cosmological Evolution of the Hard X-ray AGN Luminosity Function and the Origin of the Hard X-ray Background
• The 2dF QSO Redshift Survey - XII. The spectroscopic catalogue and luminosity function
• Luminosity-dependent evolution of soft X-ray selected AGN: New Chandra and XMM-Newton surveys
• The Cosmic Evolution of Hard X-ray Selected Active Galactic Nuclei
• High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data IV: Luminosity Function from the Fall Equatorial Stripe Sampl
• X-ray emission from radio-quiet quasars in the SDSS Early Data Release. The alpha_ox dependence upon UV luminosity
• The HELLAS2XMM survey: IV. Optical identifications and the evolution of the accretion luminosity in the Universe
• Soft X-ray and Ultraviolet Emission Relations in Optically Selected AGN Samples
• The Redshift Evolution of the 2-8 keV X-ray Luminosity Function
• X-ray Lighthouses of the High-Redshift Universe. II. Further Snapshot Observations of the Most Luminous z>4 Quasars with Chandra
• Chandra Survey of Radio-quiet, High-redshift Quasars
• Chandra and XMM-Newton observations of the first quasars: X-rays from the age of cosmic enlightenment
• Co-moving space density of X-ray-selected Active Galactic Nuclei
• High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data V. Hobby-Eberly Telescope Observations
• Exploratory Chandra Observations of the Highest-Redshift Quasars: X-rays from the Dawn of the Modern Universe
• X-ray lighthouses of the high-redshift Universe. Probing the most luminous z>4 Palomar Digital Sky Survey Quasars with Chandra

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