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高精度X射线logN-logS分布:对模糊AGN人群的影响

High precision X-ray logN-logS distributions: implications for the obscured AGN population

S. Mateos, R. S. Warwick, F. J. Carrera, G. C. Stewart, J. Ebrero, R. Della Ceca, A. Caccianiga, R. Gilli, M. J. Page, E. Treister, J. A. Tedds, M. G. Watson, G… 展开作者

S. Mateos, R. S. Warwick, F. J. Carrera, G. C. Stewart, J. Ebrero, R. Della Ceca, A. Caccianiga, R. Gilli, M. J. Page, E. Treister, J. A. Tedds, M. G. Watson, G. Lamer, R. D. Saxton, H. Brunner, C. G. Page

摘要:

我们已经限制了河外源计数分布在一个广泛的范围内的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。我们使用了|b| >20 deg、覆盖132.3 deg^2天区的1129个XMM-牛顿观测数据,收集了迄今为止在0.5-1 keV、1-2 keV、2-4.5 keV、4.5-10 keV、0.5-2 keV和2-10 keV能量带的最大完整X射线天体样本。我们的调查包括超过30,000个源,在2 keV以下低至~10^{-15} erg/cm^2/s,在2 keV以上低至~10^{-14} erg/cm^2/s。除了4.5-10 keV带外,在所有能带中都检测到源计数分布的中断。包含2个幂律分量的分析模型不能充分描述在源计数分布中看到的曲率。logN(>S)-logS的形状强烈地依赖于能带,随着我们向更高能量移动,通常明显变陡。这是由于非活动星系核的星群,主要由恒星和星系团组成,在能量为<2 keV and at fluxes >10^{-13} erg/cm^2/s时贡献了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射线源的相对比例有实质性增加,从低于2 keV的&gt;55%增加到高于2 keV的&gt;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。

英文摘要:

We have constrained 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. We have used 1129 XMM-Newton observations at |b|>20 deg covering a sky area of 132.3 deg^2 to compile the largest complete samples of X-ray objects to date in the 0.5-1 keV, 1-2 keV, 2-4.5 keV, 4.5-10 keV, 0.5-2 keV and 2-10 keV energy bands. Our survey includes in excess of 30,000 sources down to ~10^-15 erg/cm^2/s below 2 keV and down to ~10^{-14} erg/cm^2/s above 2 keV. A break in the source count distributions was detected in all energy bands except the 4.5-10 keV band. 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 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, 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.

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