X-ray spectral properties of active galactic nuclei in the Chandra
X-ray spectral properties of active galactic nuclei in the Chandra
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2006
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通讯作者：
P. Tozzi;R. Gilli;V. Mainieri;G. Risaliti;P. Rosati;S. Borgani;R. Giacconi;G. Hasinger;M. Nonino;A. Streblyanska;W. Zheng
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作者：
P. Tozzi;R. Gilli;V. Mainieri;G. Risaliti;P. Rosati;S. Borgani;R. Giacconi;G. Hasinger;M. Nonino;A. Streblyanska;W. Zheng
我们对钱德拉深场南（CDFS） 1Ms目录中的源进行了详细的x射线光谱分析，利用光学光谱和光度红移对347个星系外源中的321个源进行了分析。作为默认的光谱模型，我们采用斜率为Γ的幂律，具有本征红移吸收NH，固定的银河系吸收和未解析的铁发射线。对于82个x射线明亮源，我们能够在不影响Γ和NH的情况下进行x射线光谱分析。幂律斜率的加权平均值为Γ 1.75±0.02，最佳拟合值分布的本征散度为σint 0.30。我们没有发现光谱指数Γ和本征吸收柱密度NH之间的相关性。然后我们研究了整个样品的吸收分布，通过固定Γ= 1.8推导出微弱光源的NH值。我们还允许在软能量下存在与主幂律斜率相同的散射分量，以及典型的康普顿厚AGN的纯反射谱。我们在8个源中检测到散射软分量的存在；我们还确定了14个显示反射主导光谱的源。后者被称为康普顿厚AGN候选者。通过校正不完备性和抽样体积效应，我们从观测值中恢复了代表整个AGN种群的内在NH分布f (NH)dNH。f （NH）呈对数正态分布，在log(NH) 23.1和σ 1.1附近达到峰值。有趣的是，这种分布显示了康普顿-薄和康普顿-厚AGN种群之间的连续性。我们发现样品中吸收源（含NH > 10 22 cm−2）的比例是恒定的（约75%的水平）或随着红移而适度增加。最后，我们将光学分类与x射线光谱特性进行了比较，确认了至少80%具有光谱识别的源（占总x射线样品的1/3），未吸收（被吸收）x射线源与光学类型I (II) AGN的对应是准确的。
We present a detailed X-ray spectral analysis of the sources in the 1Ms catalog of the Chandra Deep Field South (CDFS) taking advantage of optical spectroscopy and photometric redshifts for 321 extragalactic sources out of the total sample of 347 sources. As a default spectral model, we adopt a power law with slope Γ with an intrinsic redshifted absorption NH, a fixed Galactic absorption and an unresolved Fe emission line. For 82 X-ray bright sources, we are able to perform the X-ray spectral analysis leaving both Γ and NH free. The weighted mean value for the slope of the power law is � Γ �� 1.75 ± 0.02, and the distribution of best fit values shows an intrinsic dispersion of σint � 0.30. We do not find hints of a correlation between the spectral index Γ and the intrinsic absorption column density NH. We then investigate the absorption distribution for the whole sample, deriving the NH values in faint sources by fixing Γ= 1.8. We also allow for the presence of a scattered component at soft energies with the same slope of the main power law, and for a pure reflection spectrum typical of Compton-thick AGN. We detect the presence of a scattered soft component in 8 sources; we also identify 14 sources showing a reflection-dominated spectrum. The latter are referred to as Compton-thick AGN candidates. By correcting for both incompleteness and sampling-volume effects, we recover the intrinsic NH distribution representative of the whole AGN population, f (NH)dNH, from the observed one. f (NH) shows a lognormal shape, peaking around log(NH) � 23.1 and with σ � 1.1. Interestingly, such a distribution shows continuity between the population of Compton-thin and that of Compton-thick AGN. We find that the fraction of absorbed sources (with NH > 10 22 cm −2 ) in the sample is constant (at the level of about 75%) or moderately increasing with redshift. Finally, we compare the optical classification to the X-ray spectral properties, confirming that the correspondence of unabsorbed (absorbed) X-ray sources to optical type I (type II) AGN is accurate for at least 80% of the sources with spectral identification (1/3 of the total X-ray sample).