%0 Generic %1 vito2019properties %A Vito, Fabio %A Brandt, William Nielsen %A Bauer, Franz Erik %A Calura, Francesco %A Gilli, Roberto %A Luo, Bin %A Shemmer, Ohad %A Vignali, Cristian %A Zamorani, Gianni %A Brusa, Marcella %A Civano, Francesca %A Comastri, Andrea %A Nanni, Riccardo %D 2019 %K library %T The X-ray properties of $z>6$ quasars: no evident evolution of accretion physics in the first Gyr of the Universe %U http://arxiv.org/abs/1908.09849 %X X-ray emission from QSOs has been used to assess SMBH accretion properties up to $z$~6. However, at $z>6$ only ~15 QSOs are covered by sensitive X-ray observations, preventing a statistically significant investigation of the X-ray properties of QSOs in the first Gyr of the Universe. We present new Chandra observations of 10 $z>6$ QSOs, selected to have virial black-hole mass estimates from Mg II line spectroscopy. Adding archival X-ray data for an additional 15 $z>6$ QSOs, we investigate the X-ray properties of the QSO population in the first Gyr of the Universe, focusing in particular on the $L_UV-L_X$ relation, which is traced by the $\alpha_ox$ parameter, and the shape of their X-ray spectra. We performed photometric analyses to derive estimates of the X-ray luminosities, and thus the $\alpha_ox$ values and bolometric corrections ($K_bol=L_bol/L_X$). We compared the resulting $\alpha_ox$ and $K_bol$ distributions with the results found for QSO samples at lower redshift. Finally, we performed a basic X-ray spectral analysis of the brightest $z>6$ QSOs to derive their individual photon indices, and joint spectral analysis of the whole sample to estimate the average photon index. We confirm a lack of significant evolution of $\alpha_ox$ with redshift, extending the results from previous works up to $z>6$, and the trend of an increasing bolometric correction with increasing luminosity found for QSOs at lower redshifts. The average power-law photon index of our sample ($\Gamma=2.20_-0.34^+0.39$ and $\Gamma=2.13_-0.13^+0.13$ for sources with $<30$ and $>30$ net counts, respectively) is slightly steeper than, but still consistent with, typical QSOs at $z=1-6$. All these results point toward a lack of substantial evolution of the inner accretion-disk/hot-corona structure in QSOs from low redshift to $z>6$. Our data hint at generally high Eddington ratios at $z>6$.

@misc{vito2019properties, abstract = {X-ray emission from QSOs has been used to assess SMBH accretion properties up to $z$~6. However, at $z>6$ only ~15 QSOs are covered by sensitive X-ray observations, preventing a statistically significant investigation of the X-ray properties of QSOs in the first Gyr of the Universe. We present new Chandra observations of 10 $z>6$ QSOs, selected to have virial black-hole mass estimates from Mg II line spectroscopy. Adding archival X-ray data for an additional 15 $z>6$ QSOs, we investigate the X-ray properties of the QSO population in the first Gyr of the Universe, focusing in particular on the $L_{UV}-L_{X}$ relation, which is traced by the $\alpha_{ox}$ parameter, and the shape of their X-ray spectra. We performed photometric analyses to derive estimates of the X-ray luminosities, and thus the $\alpha_{ox}$ values and bolometric corrections ($K_{bol}=L_{bol}/L_{X}$). We compared the resulting $\alpha_{ox}$ and $K_{bol}$ distributions with the results found for QSO samples at lower redshift. Finally, we performed a basic X-ray spectral analysis of the brightest $z>6$ QSOs to derive their individual photon indices, and joint spectral analysis of the whole sample to estimate the average photon index. We confirm a lack of significant evolution of $\alpha_{ox}$ with redshift, extending the results from previous works up to $z>6$, and the trend of an increasing bolometric correction with increasing luminosity found for QSOs at lower redshifts. The average power-law photon index of our sample ($\Gamma=2.20_{-0.34}^{+0.39}$ and $\Gamma=2.13_{-0.13}^{+0.13}$ for sources with $<30$ and $>30$ net counts, respectively) is slightly steeper than, but still consistent with, typical QSOs at $z=1-6$. All these results point toward a lack of substantial evolution of the inner accretion-disk/hot-corona structure in QSOs from low redshift to $z>6$. Our data hint at generally high Eddington ratios at $z>6$.}, added-at = {2019-08-28T05:11:01.000+0200}, author = {Vito, Fabio and Brandt, William Nielsen and Bauer, Franz Erik and Calura, Francesco and Gilli, Roberto and Luo, Bin and Shemmer, Ohad and Vignali, Cristian and Zamorani, Gianni and Brusa, Marcella and Civano, Francesca and Comastri, Andrea and Nanni, Riccardo}, biburl = {https://www.bibsonomy.org/bibtex/231516d8afa85b0d8521dbdd8cf31d39d/gpkulkarni}, description = {The X-ray properties of $z>6$ quasars: no evident evolution of accretion physics in the first Gyr of the Universe}, interhash = {98d911d28b1afe18a79b1217acaa2d79}, intrahash = {31516d8afa85b0d8521dbdd8cf31d39d}, keywords = {library}, note = {cite arxiv:1908.09849Comment: 15 pages. 10 figures. 7 tables. Accepted for publication in A&A}, timestamp = {2019-08-28T05:11:01.000+0200}, title = {The X-ray properties of $z>6$ quasars: no evident evolution of accretion physics in the first Gyr of the Universe}, url = {http://arxiv.org/abs/1908.09849}, year = 2019 }