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arXiv 1603.04852astro-ph.HEastro-ph.COastro-ph.GA
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局域宇宙中的康普顿厚吸积

Compton-thick Accretion in the local Universe

C. Ricci, Y. Ueda, M. J. Koss, B. Trakhtenbrot, F. E. Bauer, P. Gandhi

摘要:

被严重遮蔽的吸积被认为是超大质量黑洞生长的一个重要阶段,并在塑造宇宙X射线背景(CXB)的观测光谱方面发挥重要作用。硬X射线(E $>$ 10 keV)选择的样品比在较低能量下选择的样品受吸收的影响更小,因此是探测和识别康普顿厚度(CT,$\log N_{\rm\,H}\geq 24$)活动星系核(AGN)的最佳方法之一。在这封信中,我们提出了最大的宽带(0.3-150千电子伏)的硬X射线选择AGN的X射线光谱研究的第一个结果,迄今为止,侧重于严重遮蔽源的属性。我们的样本包括在全天空硬X射线Swift/BAT巡天的70个月星表中报告的834个活动星系核(728个非耀变体,平均红移$z\simeq 0.055$)。我们发现了55个CT活动星系核,它们代表了我们的非耀变体的$7.6^{+1.1}_{-2.1}\%$。其中26个是首次被报道为候选CT活动星系核。我们对选择偏差进行了修正,并导出了两个不同光度范围内活动星系核在局域宇宙中的内禀柱密度分布。我们发现随着亮度的增加,暗康普顿薄活动星系核的比例显著减少,从$46\pm3\%$(对于$\log L_{\rm\,14-195} = 40-43.7$)到$39\pm3\%$(对于$\log L_{\rm\,14-195} = 43.7-46$)。CT AGN也有类似的趋势。在$\log N_{\rm H} = 20-25$范围内,将$\log N_{\rm\,H}=24-25$归一化为1的CT活动星系核的本征分数为$27\pm4\%$,这与位于20 Mpc范围内的活动星系核的观测值一致。

英文摘要:

Heavily obscured accretion is believed to represent an important stage in the growth of supermassive black holes, and to play an important role in shaping the observed spectrum of the Cosmic X-ray Background (CXB). Hard X-ray (E$>$10 keV) selected samples are less affected by absorption than samples selected at lower energies, and are therefore one of the best ways to detect and identify Compton-thick (CT, $\log N_{\rm\,H}\geq 24$) Active Galactic Nuclei (AGN). In this letter we present the first results of the largest broad-band (0.3-150 keV) X-ray spectral study of hard X-ray selected AGN to date, focusing on the properties of heavily obscured sources. Our sample includes the 834 AGN (728 non-blazar, average redshift $z\simeq 0.055$) reported in the 70-months catalog of the all-sky hard X-ray Swift/BAT survey. We find 55 CT AGN, which represent $7.6^{+1.1}_{-2.1}\%$ of our non-blazar sample. Of these, 26 are reported as candidate CT AGN for the first time. We correct for selection bias and derive the intrinsic column density distribution of AGN in the local Universe in two different luminosity ranges. We find a significant decrease in the fraction of obscured Compton-thin AGN for increasing luminosity, from $46\pm3\%$ (for $\log L_{\rm\,14-195} = 40-43.7$) to $39\pm3\%$ (for $\log L_{\rm\,14-195} = 43.7-46$). A similar trend is also found for CT AGN. The intrinsic fraction of CT AGN with $\log N_{\rm\,H}=24-25$ normalised to unity in the $\log N_{\rm H} = 20-25$ range is $27\pm4\%$, and is consistent with the observed value obtained for AGN located within 20 Mpc.

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