We present a systematic analysis of X-ray archival data of all the 29 quasars
(QSOs) at $z$ > 5.5 observed so far with Chandra, XMM-Newton and Swift-XRT,
including the most-distant quasar ever discovered, ULAS J1120+0641 ($z$ =
7.08). This study allows us to place constraints on the mean spectral
properties of the primordial population of luminous Type 1 (unobscured)
quasars. Eighteen quasars are detected in the X-ray band, and we provide
spectral-fitting results for their X-ray properties, while for the others we
provide upper limits to their soft (0.5-2.0 keV) X-ray flux. We measured the
power-law photon index and derived an upper limit to the column density for the
five quasars (J1306+0356, J0100+2802, J1030+0524, J1148+5251, J1120+0641) with
the best spectra (> 30 net counts in the 0.5-7.0 keV energy range) and find
that they are consistent with values from the literature and lower-redshift
quasars. By stacking the spectra of ten quasars detected by Chandra in the
redshift range 5.7 $łe$ $z$ $łe$ 6.1 we find a mean X-ray power-law photon
index of $\Gamma = 1.92_-0.27^+0.28$ and a neutral intrinsic absorption
column density of $N_H 10^23$ cm$^-2$. These results suggest that the
X-ray spectral properties of luminous quasars have not evolved up to $z$
$\approx$ 6. We also derived the optical-X-ray spectral slopes ($\alpha_ox$)
of our sample and combined them with those of previous works, confirming that
$\alpha_ox$ strongly correlates with UV monochromatic luminosity at 2500 \AA
. These results strengthen the non-evolutionary scenario for the spectral
properties of luminous active galactic nuclei (AGN).
Description
[1704.08693] The X-ray properties of z$\sim$6 luminous quasars
%0 Generic
%1 nanni2017properties
%A Nanni, R.
%A Vignali, C.
%A Gilli, R.
%A Moretti, A.
%A Brandt, W. N.
%D 2017
%K high-z quasars x-ray
%T The X-ray properties of z$\sim$6 luminous quasars
%U http://arxiv.org/abs/1704.08693
%X We present a systematic analysis of X-ray archival data of all the 29 quasars
(QSOs) at $z$ > 5.5 observed so far with Chandra, XMM-Newton and Swift-XRT,
including the most-distant quasar ever discovered, ULAS J1120+0641 ($z$ =
7.08). This study allows us to place constraints on the mean spectral
properties of the primordial population of luminous Type 1 (unobscured)
quasars. Eighteen quasars are detected in the X-ray band, and we provide
spectral-fitting results for their X-ray properties, while for the others we
provide upper limits to their soft (0.5-2.0 keV) X-ray flux. We measured the
power-law photon index and derived an upper limit to the column density for the
five quasars (J1306+0356, J0100+2802, J1030+0524, J1148+5251, J1120+0641) with
the best spectra (> 30 net counts in the 0.5-7.0 keV energy range) and find
that they are consistent with values from the literature and lower-redshift
quasars. By stacking the spectra of ten quasars detected by Chandra in the
redshift range 5.7 $łe$ $z$ $łe$ 6.1 we find a mean X-ray power-law photon
index of $\Gamma = 1.92_-0.27^+0.28$ and a neutral intrinsic absorption
column density of $N_H 10^23$ cm$^-2$. These results suggest that the
X-ray spectral properties of luminous quasars have not evolved up to $z$
$\approx$ 6. We also derived the optical-X-ray spectral slopes ($\alpha_ox$)
of our sample and combined them with those of previous works, confirming that
$\alpha_ox$ strongly correlates with UV monochromatic luminosity at 2500 \AA
. These results strengthen the non-evolutionary scenario for the spectral
properties of luminous active galactic nuclei (AGN).
@misc{nanni2017properties,
abstract = {We present a systematic analysis of X-ray archival data of all the 29 quasars
(QSOs) at $z$ > 5.5 observed so far with Chandra, XMM-Newton and Swift-XRT,
including the most-distant quasar ever discovered, ULAS J1120+0641 ($z$ =
7.08). This study allows us to place constraints on the mean spectral
properties of the primordial population of luminous Type 1 (unobscured)
quasars. Eighteen quasars are detected in the X-ray band, and we provide
spectral-fitting results for their X-ray properties, while for the others we
provide upper limits to their soft (0.5-2.0 keV) X-ray flux. We measured the
power-law photon index and derived an upper limit to the column density for the
five quasars (J1306+0356, J0100+2802, J1030+0524, J1148+5251, J1120+0641) with
the best spectra (> 30 net counts in the 0.5-7.0 keV energy range) and find
that they are consistent with values from the literature and lower-redshift
quasars. By stacking the spectra of ten quasars detected by Chandra in the
redshift range 5.7 $\le$ $z$ $\le$ 6.1 we find a mean X-ray power-law photon
index of $\Gamma = 1.92_{-0.27}^{+0.28}$ and a neutral intrinsic absorption
column density of $N_H \le 10^{23}$ cm$^{-2}$. These results suggest that the
X-ray spectral properties of luminous quasars have not evolved up to $z$
$\approx$ 6. We also derived the optical-X-ray spectral slopes ($\alpha_{ox}$)
of our sample and combined them with those of previous works, confirming that
$\alpha_{ox}$ strongly correlates with UV monochromatic luminosity at 2500 \AA
. These results strengthen the non-evolutionary scenario for the spectral
properties of luminous active galactic nuclei (AGN).},
added-at = {2017-05-01T10:12:29.000+0200},
author = {Nanni, R. and Vignali, C. and Gilli, R. and Moretti, A. and Brandt, W. N.},
biburl = {https://www.bibsonomy.org/bibtex/222fc58327ae8b5f6c9b58650b978d0de/miki},
description = {[1704.08693] The X-ray properties of z$\sim$6 luminous quasars},
interhash = {6093f7175470d631f251c7e3fba0428f},
intrahash = {22fc58327ae8b5f6c9b58650b978d0de},
keywords = {high-z quasars x-ray},
note = {cite arxiv:1704.08693Comment: 12 pages, 7 figures, accepted for publication in Astronomy and Astrophysics},
timestamp = {2017-05-01T10:12:29.000+0200},
title = {The X-ray properties of z$\sim$6 luminous quasars},
url = {http://arxiv.org/abs/1704.08693},
year = 2017
}