在COSMOS场中追踪高度模糊的类星体
Chasing highly obscured QSOs in the COSMOS field
摘要：
我们利用深钱德拉和斯皮策覆盖的大面积（超过10倍的钱德拉深场覆盖的面积，COSMOS领域的CDF，将高度模糊的，康普顿厚度的活动核的搜索扩展到更高的亮度。这些源的表面密度很低，只有通过大面积调查，如COSMOS调查，才能提供大样本。我们分析了24 $μ$ m通量大于550 $μ$ Jy的COSMOS MIPS源的X射线性质。对于在钱德拉图像中没有直接检测到的MIPS源，我们在软X射线和硬X射线波段产生堆叠图像。为了估计康普顿厚的活动星系核在MIPS源人口的比例，我们比较观察到的堆叠计数率和硬度比的预测详细的蒙特卡罗模拟，包括模糊的活动星系核和恒星形成的星系。在z=0.7- 1.2范围内，低光度康普顿厚度活动星系核（logL（2- 10 keV）=43.5-44）的密度为$(3.7\pm1.1) \times10^{-5}$ Mpc $^{-3}$，相当于X射线选择活动星系核的密度的$\sim67%$。在高光度和低光度下，红外选择的、康普顿厚的活动星系核与X射线选择的、未遮蔽的和中度遮蔽的活动星系核的比例之间的比较表明，康普顿厚的活动星系核遵循与康普顿薄的活动星系核相似的光度依赖性，在高光度下变得相对罕见。我们估计活动星系核（无遮蔽，中度遮蔽和康普顿厚）的总MIPS源人口的分数是$49\pm10%$，一个值显着高于以前估计的类似24 $μ$米通量。我们将讨论我们的研究结果如何约束活动星系核反馈模型。
英文摘要：
(abridged) We take advantage of the deep Chandra and Spitzer coverage of a large area (more than 10 times the area covered by the Chandra deep fields, CDFs in the COSMOS field, to extend the search of highly obscured, Compton-thick active nuclei to higher luminosity. These sources have low surface density and large samples can be provided only through large area surveys, like the COSMOS survey. We analyze the X-ray properties of COSMOS MIPS sources with 24$μ$m fluxes higher than 550$μ$Jy. For the MIPS sources not directly detected in the Chandra images we produce stacked images in soft and hard X-rays bands. To estimate the fraction of Compton-thick AGN in the MIPS source population we compare the observed stacked count rates and hardness ratios to those predicted by detailed Monte Carlo simulations including both obscured AGN and star-forming galaxies. The density of lower luminosity Compton-thick AGN (logL(2-10keV)=43.5-44) at z=0.7--1.2 is $(3.7\pm1.1) \times10^{-5}$ Mpc$^{-3}$, corresponding to $\sim67%$ of that of X-ray selected AGN. The comparison between the fraction of infrared selected, Compton thick AGN to the X-ray selected, unobscured and moderately obscured AGN at high and low luminosity suggests that Compton-thick AGN follow a luminosity dependence similar to that discovered for Compton-thin AGN, becoming relatively rarer at high luminosities. We estimate that the fraction of AGN (unobscured, moderately obscured and Compton thick) to the total MIPS source population is $49\pm10%$, a value significantly higher than that previously estimated at similar 24$μ$m fluxes. We discuss how our findings can constrain AGN feedback models.
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