High precision X-ray log N – log S distributions: implications for the obscured AGN population
High precision X-ray log N – log S distributions: implications for the obscured AGN population
复制标题
高精度 X 射线 log N – log S 分布：对模糊 AGN 群体的影响
DOI：
--
复制
发表时间：
2008
期刊：
影响因子：
--
通讯作者：
C. Page
中科院分区：
文献类型：
--
作者：
S. Mateos;R. Warwick;F. J. Carrera;G. Stewart;J. Ebrero;J. Ebrero;R. Ceca;A. Caccianiga;R. Gilli;M. Page;E. Treister;J. Tedds;M. Watson;G. Lamer;R. Saxton;H. Brunner;C. Page
上下文我们对活动星系核的性质，特别是光学第二类天体的性质的了解是非常不完整的。由于河外源数分布依赖于活动星系核的宇宙学和统计学性质，因此它们提供了一种直接的方法来研究潜在的源群。目标。我们的目标是约束河外源计数分布在广泛的X射线通量和各种能量带，以测试是否从X射线背景合成模型的预测同意与我们的测量提供的观测约束。方法.我们使用了1129个XMM-牛顿观测数据，|B|> 20千分之一，覆盖132.3平方度的天空总面积，以汇编迄今为止最大的X射线选定天体的完整样本，这些样本在标准XMM-牛顿数据处理中使用的0.5− 1 k eV，1− 2k eV，2−4.5 keV，4.5−10 keV波段以及在源计数研究中更常考虑的0.5−2 keV和2−10 keV能带。我们的调查包括超过30 000个源，其通量范围在2 keV以下为10 - 15至10 - 12 erg cm-2 s-1，在2 keV以上为10 - 14至10 - 12 erg cm-2 s-1，宇宙X射线背景能量密度的大部分都是在那里产生的。结果我们获得的非常大的样本量意味着我们的结果不受宇宙方差或低计数统计的限制。除了4.5 - 10 keV带之外，在所有能带中都检测到源计数分布的突变。我们发现，一个分析模型，包括2个幂律分量不能充分描述的曲率中看到的源计数分布。logN（>S）-logS的形状强烈依赖于能带，随着我们向更高能量移动，一般会明显变陡。这是因为非活动星系核的星群，主要由恒星和星系团组成，在能量小于2 keV和通量大于等于10 −13 erg cm −2 s −1的情况下，贡献了30%的源星群，并且这些星群的源计数分布比活动星系核要平坦得多。我们发现在较高能量下硬X射线源的相对比例大幅增加，从低于2 keV的≥55%增加到高于2 keV的≥77%。然而，在4.5 keV以上检测到的大多数源在2 keV以下仍然具有显著的通量。与合成模型的预测比较表明，模型可能会过度预测微弱吸收的活动星系核的数量，这将需要对一些模型参数进行微调，例如模糊的活动星系核与未模糊的活动星系核的比率和/或在中等模糊度下的柱密度分布。
Context. Our knowledge of the properties of AGN, especially those of optical type-2 objects, is very incomplete. Because extragalactic source count distributions are dependent on the cosmological and statistical properties of AGN, they provide a direct method of investigating the underlying source populations. Aims. We aim to constrain the extragalactic source count distributions over a broad range of X-ray fluxes and in various energy bands to test whether the predictions from X-ray background synthesis models agree with the observational constraints provided by our measurements. Methods. We have used 1129 XMM-Newton observations at |b| > 20 ◦ covering a total sky area of 132.3 deg 2 to compile the largest complete samples of X-ray selected objects to date both in the 0.5− 1k eV, 1− 2k eV, 2−4.5 keV, 4.5−10 keV bands employed in standard XMM-Newton data processing and in the 0.5−2 keV and 2−10 keV energy bands more usually considered in source count studies. Our survey includes in excess of 30 000 sources and spans fluxes from ∼10 −15 to 10 −12 erg cm −2 s −1 below 2 keV and from ∼10 −14 to 10 −12 erg cm −2 s −1 above 2 keV where the bulk of the cosmic X-ray background energy density is produced. Results. The very large sample size we obtained means our results are not limited by cosmic variance or low counting statistics. A break in the source count distributions was detected in all energy bands except the 4.5−10 keV band. We find that an analytical model comprising 2 power-law components cannot adequately describe the curvature seen in the source count distributions. The shape of the logN(>S ) − logS is strongly dependent on the energy band with a general steepening apparent as we move to higher energies. This is due to the fact that non-AGN populations, comprised mainly of stars and clusters of galaxies, contribute up to 30% of the source population at energies <2 keV and at fluxes ≥10 −13 erg cm −2 s −1 , and these populations of objects have significantly flatter source count distributions than AGN. We find a substantial increase in the relative fraction of hard X-ray sources at higher energies, from ≥55% below 2 keV to ≥77% above 2 keV. However, the majority of sources detected above 4.5 keV still have significant flux below 2 keV. Comparison with predictions from the synthesis models suggest that the models might be overpredicting the number of faint absorbed AGN, which would call for fine adjustment of some model parameters such as the obscured to unobscured AGN ratio and/or the distribution of column densities at intermediate obscuration.