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arXiv 1704.08693astro-ph.GA
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z $\sim$ 6亮类星体的X射线性质

The X-ray properties of z$\sim$6 luminous quasars

R. Nanni, C. Vignali, R. Gilli, A. Moretti, W. N. Brandt

摘要:

我们提出了一个系统的X射线档案数据的所有29个类星体(类星体)在$z$ > 5.5的钱德拉,XMM-Newton和Swift-XRT,包括迄今发现的最遥远的类星体,ULAS J1120+0641($z$ = 7.08)。这项研究使我们能够将约束的原始人口的发光1型(未遮蔽)类星体的平均光谱特性。在X射线波段探测到了18个类星体,我们提供了它们的X射线特性的光谱拟合结果,而对于其他类星体,我们提供了它们的软(0.5-2.0 keV)X射线通量的上限。我们测量了幂律光子指数,并推导出了这五个类星体的柱密度上限(J1306+0356,J0100+2802,J1030+0524,J1148+5251,J1120+0641)具有最佳光谱(在0.5-7.0 keV能量范围内> 30个净计数),并发现它们与文献和低红移类星体的值一致。通过叠加钱德拉探测到的红移范围为5.7 $\le$ 6.1的10个类星体的光谱,我们发现平均X射线幂律光子指数为$z$,中性本征吸收柱密度为$N_H \le 10^{23}$ cm $^{-2}$。这些结果表明,发光类星体的X射线光谱特性尚未演化到$z$ $\approx$ 6。我们还导出了我们样品的光学X射线光谱斜率($α_{ox}$),并将它们与以前的工作相结合,证实了$α_{ox}$与2500 nm处的紫外单色光度密切相关。这些结果强化了发光活动星系核(AGN)光谱特性的非演化情景。

英文摘要:

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 $Γ= 1.92_{-0.27}^{+0.28}$ 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 ($α_{ox}$) of our sample and combined them with those of previous works, confirming that $α_{ox}$ strongly correlates with UV monochromatic luminosity at 2500 Å. These results strengthen the non-evolutionary scenario for the spectral properties of luminous active galactic nuclei (AGN).

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