钱德拉COSMOS遗产巡天：宇宙X射线背景的能谱和对未探测粒子群的限制
The Chandra COSMOS legacy survey: Energy Spectrum of the Cosmic X-ray Background and constraints on undetected populations
摘要：
使用{ \em钱德拉}观测在2.15度$^{2}$ COSMOS遗产领域，我们提出了一个最准确的测量宇宙X射线背景（CXB）光谱的日期在[0.3-7] keV的能量带。CXB有三个不同的组成部分：来自两个银河系碰撞热等离子体在kT $\sim$ 0.27和0.07千电子伏和河外幂律与光子光谱指数$Γ$ =1.45 $\pm{0.02}$的贡献。河外分量的1 keV标准化为10.91 $\pm{0.16}$ keV cm $^{-2}$ s $^{-1}$ sr $^{-1}$ keV $^{-1}$。去除所有X射线探测源，剩余的未分辨CXB通过幂律最佳拟合，归一化为4.18 $\pm{0.26}$ keV cm $^{-2}$ s $^{-1}$ sr $^{-1}$ keV $^{-1}$，光子谱指数$Γ$ =1.57 $\pm{0.10}$。去除暗星系到i $_{AB}\sim$ 27-28留下了硬光谱，$Γ\sim$为1.25，$\sim$为1.37 keV cm $^{-2}$ s $^{-1}$ sr $^{-1}$ keV $^{-1}$。这意味着观测到的CXB的$\sim$ 91%被分解为探测到的X射线源和未探测到的星系。贡献总CXB的$\sim 8-9\%$的未解析来源显示出比解析来源更难且可能更模糊的边缘证据。CXB的另一个$\sim$ 1可以归因于尚未被发现的恒星形成星系和被吸收的活动星系核。根据这些限制，我们研究了一种情况下，早期黑洞完全占非源CXB分数和限制他们的一些性质。为了不超过剩余的CXB和$z\sim$ 6的吸积质量密度，这样的黑洞群必须在康普顿厚度的包络中生长，N $_{H}>$ 1.6 $\times$ 10 $^{25}$ cm $^{-2}$，并在极低金属丰度的环境$(Z_\odot)\sim10^{-3}$中形成。
英文摘要：
Using {\em Chandra} observations in the 2.15 deg$^{2}$ COSMOS legacy field, we present one of the most accurate measurements of the Cosmic X-ray Background (CXB) spectrum to date in the [0.3-7] keV energy band. The CXB has three distinct components: contributions from two Galactic collisional thermal plasmas at kT$\sim$0.27 and 0.07 keV and an extragalactic power-law with photon spectral index $Γ$=1.45$\pm{0.02}$. The 1 keV normalization of the extragalactic component is 10.91$\pm{0.16}$ keV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ keV$^{-1}$. Removing all X-ray detected sources, the remaining unresolved CXB is best-fit by a power-law with normalization 4.18$\pm{0.26}$ keV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ keV$^{-1}$ and photon spectral index $Γ$=1.57$\pm{0.10}$. Removing faint galaxies down to i$_{AB}\sim$27-28 leaves a hard spectrum with $Γ\sim$1.25 and a 1 keV normalization of $\sim$1.37 keV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ keV$^{-1}$. This means that $\sim$91\% of the observed CXB is resolved into detected X-ray sources and undetected galaxies. Unresolved sources that contribute $\sim 8-9\%$ of the total CXB show a marginal evidence of being harder and possibly more obscured than resolved sources. Another $\sim$1\% of the CXB can be attributed to still undetected star forming galaxies and absorbed AGN. According to these limits, we investigate a scenario where early black holes totally account for non source CXB fraction and constrain some of their properties. In order to not exceed the remaining CXB and the $z\sim$6 accreted mass density, such a population of black holes must grow in Compton-thick envelopes with N$_{H}>$1.6$\times$10$^{25}$ cm$^{-2}$ and form in extremely low metallicity environments $(Z_\odot)\sim10^{-3}$.
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