AEGIS：X射线和光学选择活动星系核的人口统计
AEGIS: Demographics of X-ray and Optically Selected AGNs
摘要：
我们发展了一种新的诊断方法，通过结合[O III]/H β比值和静止坐标系U-B色，将星系分为活动星系核宿主星系、恒星形成星系和吸收主导星系。这可以用来在中等红移（z<1）的星系样本中鲁棒地选择活动星系核。我们利用从DEEP 2星系红移巡天和全波长扩展的增长带国际巡天（AEGIS）中选取的3150个星系（0.3<z<0.8，IAB <22），比较了光学选择和X射线选择的结果。在这个样本中的146个X射线源中，有58%在光学上被归类为发射线活动星系核，其余的被归类为恒星形成星系或吸收支配星系。后者也被称为“X射线明亮的光学正常星系”（XBONG）。光学发射线与X射线性质之间关系的分析表明，光学活动星系核选择的完整性取决于恒星形成速率和观测光谱的质量。它还表明，XBONG似乎并不是一个物理上不同的人口从其他X射线检测，发射线活动星系核。另一方面，X射线活动星系核的选择也有很强的偏向性。在我们的样本中，大约有2/3的L_bol>10^44 erg/s的发射线活动星系核在我们的200 ks钱德拉图像中没有被探测到，这很可能是由于活动星系核附近气体的中等或严重吸收。在z~0.6处的2- 7 keV Seyfert 2s的探测率表明它们的柱密度分布和康普顿厚部分与本地Seyfert相似。需要多种样品选择技术来获得尽可能完整的样品。
英文摘要：
We develop a new diagnostic method to classify galaxies into AGN hosts, star-forming galaxies, and absorption-dominated galaxies by combining the [O III]/Hbeta ratio with rest-frame U-B color. This can be used to robustly select AGNs in galaxy samples at intermediate redshifts (z<1). We compare the result of this optical AGN selection with X-ray selection using a sample of 3150 galaxies with 0.3<z<0.8 and I_AB<22, selected from the DEEP2 Galaxy Redshift Survey and the All-wavelength Extended Groth Strip International Survey (AEGIS). Among the 146 X-ray sources in this sample, 58% are classified optically as emission-line AGNs, the rest as star-forming galaxies or absorption-dominated galaxies. The latter are also known as "X-ray bright, optically normal galaxies" (XBONGs). Analysis of the relationship between optical emission lines and X-ray properties shows that the completeness of optical AGN selection suffers from dependence on the star formation rate and the quality of observed spectra. It also shows that XBONGs do not appear to be a physically distinct population from other X-ray detected, emission-line AGNs. On the other hand, X-ray AGN selection also has strong bias. About 2/3 of all emission-line AGNs at L_bol>10^44 erg/s in our sample are not detected in our 200 ks Chandra images, most likely due to moderate or heavy absorption by gas near the AGN. The 2--7 keV detection rate of Seyfert 2s at z~0.6 suggests that their column density distribution and Compton-thick fraction are similar to that of local Seyferts. Multiple sample selection techniques are needed to obtain as complete a sample as possible.
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