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arXiv 1709.07892astro-ph.GA
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钱德拉深场中的高红移AGN:次$L_*$粒子群的遮蔽分数和空间密度

High-redshift AGN in the Chandra Deep Fields: the obscured fraction and space density of the sub-$L_*$ population

F. Vito, W. N. Brandt, G. Yang, R. Gilli, B. Luo, C. Vignali, Y. Q. Xue, A. Comastri, A. M. Koekemoer, B. D. Lehmer, T. Liu, M. Paolillo, P. Ranalli, D. P. Schn… 展开作者

F. Vito, W. N. Brandt, G. Yang, R. Gilli, B. Luo, C. Vignali, Y. Q. Xue, A. Comastri, A. M. Koekemoer, B. D. Lehmer, T. Liu, M. Paolillo, P. Ranalli, D. P. Schneider, O. Shemmer, M. Volonteri, J. Wang

摘要:

我们研究了在两个最深的X射线巡天,7 Ms \textit{Chandra}深场南和2 Ms \textit{Chandra}深场北中选择的高红移($3\leq z < 6$)活动星系核的人口。他们杰出的灵敏度和微弱源的光谱特性使我们能够专注于亚$L_*$制度(日志$L_{\mathrm{X}}\lesssim44$),以前的作品使用浅数据采样差,和模糊的人口。在充分考虑各个光度-红移概率分布函数的情况下,最终的样品由位于$3\leq z < 6$的$\approx102$ X射线选择活动星系核组成。一旦考虑到不完全性效应,活动星系核被柱密度log $N_{\mathrm{H}}>23$遮蔽的部分是$\sim0.6-0.8$,对红移和光度没有很强的依赖性。我们推导了高红移活动星系核数计数到$F_{\mathrm{0.5-2\,keV}}=7\times10^{-18}\,\mathrm{erg\,cm^{-2}\,s^{-1}}$,将以前的结果扩展到更微弱的通量,特别是在$z>4$。我们把最严格的限制,迄今为止的活动星系核光度函数在高红移的低光度端。特别是在$z>3$,空间密度在所有光度下都下降,只有低光度活动星系核的斜率稍微陡一些。通过比较活动星系核和星系密度的演变,我们认为,这种下降在高光度主要是由潜在的星系人口,而在低光度有线索的内在演变的参数驱动核活动。此外,黑洞吸积率密度和恒星形成率密度,这通常被发现在$z\lesssim3$类似地演变,似乎在更高的红移发散。

英文摘要:

We investigate the population of high-redshift ($3\leq z < 6$) AGN selected in the two deepest X-ray surveys, the 7 Ms \textit{Chandra} Deep Field-South and 2 Ms \textit{Chandra} Deep Field-North. Their outstanding sensitivity and spectral characterization of faint sources allow us to focus on the sub-$L_*$ regime (log$L_{\mathrm{X}}\lesssim44$), poorly sampled by previous works using shallower data, and the obscured population. Taking fully into account the individual photometric-redshift probability distribution functions, the final sample consists of $\approx102$ X-ray selected AGN at $3\leq z < 6$. The fraction of AGN obscured by column densities log$N_{\mathrm{H}}>23$ is $\sim0.6-0.8$, once incompleteness effects are taken into account, with no strong dependence on redshift or luminosity. We derived the high-redshift AGN number counts down to $F_{\mathrm{0.5-2\,keV}}=7\times10^{-18}\,\mathrm{erg\,cm^{-2}\,s^{-1}}$, extending previous results to fainter fluxes, especially at $z>4$. We put the tightest constraints to date on the low-luminosity end of AGN luminosity function at high redshift. The space-density, in particular, declines at $z>3$ at all luminosities, with only a marginally steeper slope for low-luminosity AGN. By comparing the evolution of the AGN and galaxy densities, we suggest that such a decline at high luminosities is mainly driven by the underlying galaxy population, while at low luminosities there are hints of an intrinsic evolution of the parameters driving nuclear activity. Also, the black-hole accretion rate density and star-formation rate density, which are usually found to evolve similarly at $z\lesssim3$, appear to diverge at higher redshifts.

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