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arXiv 1409.6918astro-ph.GAastro-ph.CO
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高红移($3<z\lesssim 5$)活动星系核的硬X射线光度函数

The Hard X-Ray Luminosity Function of High-Redshift ($3<z\lesssim 5$) Active Galactic Nuclei

Fabio Vito, Roberto Gilli, Cristian Vignali, Andrea Comastri, Marcella Brusa, Nico Cappelluti, Kazushi Iwasawa

摘要:

本文给出了高红移活动星系核(AGN)$0.5-2\,\mathrm{keV}$带选的硬带($2-10\,\mathrm{keV}$)X射线光度函数(HXLF)。为了在$ L_X - z$平面上对不同区域进行取样,我们在$3<z\lesssim5$收集了141个来自不同尺寸和深度的X射线测量的活动星系核样品。HXLF是通过最大似然法在$\mathrm{logL_X\sim43-45}$范围内与标准分析进化模型拟合的。HXLF的演化可以用纯密度演化来描述,活动星系核的空间密度从$z=3$下降到5。亮度依赖的密度演化模型,通常,最好的代表在较低的红移HXLF的演化,也是符合的数据,但一个更大的低光度($\mathrm{logL_X}<44$),高红移活动星系核的样本是必要的,以约束这个模型。我们还估计了活动星系核被柱密度$\mathrm{logN_H}\geq23$遮蔽的本征分数为$0.54\pm0.05$,对光度没有很强的依赖性。这个分数高于本地宇宙的值,表明发光($\mathrm{L_X>10^{44}\mathrm{erg\,s^{-1}}}$)遮蔽活动星系核分数从$z=0$到$z>3$的演化。

英文摘要:

We present the hard-band ($2-10\,\mathrm{keV}$) X-ray luminosity function (HXLF) of $0.5-2\,\mathrm{keV}$ band selected AGN at high redshift. We have assembled a sample of 141 AGN at $3<z\lesssim5$ from X-ray surveys of different size and depth, in order to sample different regions in the $ L_X - z$ plane. The HXLF is fitted in the range $\mathrm{logL_X\sim43-45}$ with standard analytical evolutionary models through a maximum likelihood procedure. The evolution of the HXLF is well described by a pure density evolution, with the AGN space density declining by a factor of $\sim10$ from $z=3$ to 5. A luminosity-dependent density evolution model which, normally, best represents the HXLF evolution at lower redshift, is also consistent with the data, but a larger sample of low-luminosity ($\mathrm{logL_X}<44$), high-redshift AGN is necessary to constrain this model. We also estimated the intrinsic fraction of AGN obscured by a column density $\mathrm{logN_H}\geq23$ to be $0.54\pm0.05$, with no strong dependence on luminosity. This fraction is higher than the value in the Local Universe, suggesting an evolution of the luminous ($\mathrm{L_X>10^{44}\mathrm{erg\,s^{-1}}}$) obscured AGN fraction from $z=0$ to $z>3$.

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