利用MAXI河外巡天再讨论活动星系核的局部X射线光度函数
Revisit of Local X-ray Luminosity Function of Active Galactic Nuclei with the MAXI Extragalactic Survey
摘要：
利用MAXI/GSC在4- 10 keV波段测得的第一个源表，构造了一个新的康普顿薄活动星系核（AGN）X射线（2- 10 keV）光度函数。在$z=0.002-0.2$上的样本由37个非耀变体AGN组成，其识别是高度（$z=0.002-0.2$）完成的。我们证实了这样的趋势，即与$N_{\rm H} > 10^{22}$ cm $^{-2}$吸收活动星系核的分数迅速减少对光度（$L_{\rm X}$），从0.73 $\pm$ 0.25在$L_{\rm X} = 10^{42-43.5}$ erg s $^{-1}$到0.12 $\pm0.09$在$L_{\rm X} = 10^{43.5-45.5}$ erg s $^{-1}$。所得到的光度函数与光滑连接的双幂律模型拟合良好，该模型的指数分别为$γ_1 = 0.84$（固定）和$γ_2 = 2.0\pm0.2$（低于和高于突变光度，$L_{*} = 10^{43.3\pm0.4}$ ergs s $^{-1}$）.虽然MAXI/GSC的结果与HEAO-1在$L_{\rm X} \gtsim 10^{43.5}$ erg s $^{-1}$上的结果吻合得很好，但它在较低的光度范围内给出了较大的数密度。通过对Swift/BAT巡天所得的2- 10 keV波段和14- 195 keV波段的光度函数的比较表明，2- 200 keV波段的平均宽带光谱应依赖于光度，对$L_{\rm X} \ltsim 10^{44}$ erg s $^{-1}$可用$Γ\sim1.7$近似，对$L_{\rm X} \gtsim 10^{44}$ erg s $^{-1}$可用$Γ\sim 2.0$近似。我们的样品中2- 10 keV和14- 195 keV带的亮度之间的相关性证实了这一趋势。我们认为，一旦考虑到这种影响，在10千电子伏以上和以下的光度函数之间没有矛盾。
英文摘要：
We construct a new X-ray (2--10 keV) luminosity function of Compton-thin active galactic nuclei (AGNs) in the local universe, using the first MAXI/GSC source catalog surveyed in the 4--10 keV band. The sample consists of 37 non-blazar AGNs at $z=0.002-0.2$, whose identification is highly ($>97%$) complete. We confirm the trend that the fraction of absorbed AGNs with $N_{\rm H} > 10^{22}$ cm$^{-2}$ rapidly decreases against luminosity ($L_{\rm X}$), from 0.73$\pm$0.25 at $L_{\rm X} = 10^{42-43.5}$ erg s$^{-1}$ to 0.12$\pm0.09$ at $L_{\rm X} = 10^{43.5-45.5}$ erg s$^{-1}$. The obtained luminosity function is well fitted with a smoothly connected double power-law model whose indices are $γ_1 = 0.84$ (fixed) and $γ_2 = 2.0\pm0.2$ below and above the break luminosity, $L_{*} = 10^{43.3\pm0.4}$ ergs s$^{-1}$, respectively. While the result of the MAXI/GSC agrees well with that of HEAO-1 at $L_{\rm X} \gtsim 10^{43.5}$ erg s$^{-1}$, it gives a larger number density at the lower luminosity range. Comparison between our luminosity function in the 2--10 keV band and that in the 14--195 keV band obtained from the Swift/BAT survey indicates that the averaged broad band spectra in the 2--200 keV band should depend on luminosity, approximated by $Γ\sim1.7$ for $L_{\rm X} \ltsim 10^{44}$ erg s$^{-1}$ while $Γ\sim 2.0$ for $L_{\rm X} \gtsim 10^{44}$ erg s$^{-1}$. This trend is confirmed by the correlation between the luminosities in the 2--10 keV and 14--195 keV bands in our sample. We argue that there is no contradiction in the luminosity functions between above and below 10 keV once this effect is taken into account.
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