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| Paper: |
Chandra Survey of Radio-quiet, High Redshift Quasars |
| Volume: |
290, Active Galactic Nuclei: from Central Engine to Host Galaxy |
| Page: |
597 |
| Authors: |
Bechtold, J. |
| Abstract: |
We have observed 17 optically selected, radio-quiet high-redshift (z > 4) quasars with the Chandra Observatory ACIS and detected 16 of them. When compared to low-redshift quasars observed with ROSAT, high redshift quasars are significantly more X-ray quiet, even when their extreme luminosity is taken into account. We also find that the X-ray spectral index of the high redshift objects is flatter than the average at low redshift. We show that these trends are predicted by models where the accretion flow is described by a cold, optically-thick accretion disk surrounded by a hot, optically thin corona, provided the viscosity alpha > = 0.1, and the high redshift quasars have black holes with masses ∼1010 solar masses, accreting material at ∼0.1 the Eddington limit. |
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