来自温热星系际介质的X射线发射：共振散射宇宙X射线背景的作用
X-ray emission from warm-hot intergalactic medium: the role of resonantly scattered cosmic X-ray background
摘要：
我们重新计算了来自温热星系际介质（WHIM）的X射线辐射，特别关注来自共振散射宇宙X射线背景（CXB）的贡献。如果CXB发射的重要部分被分解为点源，则WHIM沿视线的性质被记录在分解源的堆叠光谱中的吸收线和剩余漫射信号中的发射线中。对于最强的谐振线，这意味着发射率的$\sim30$提高的因素相比，在密度-温度参数空间区域的主要部分的WHIM相关的固有发射率。0.5-1 keV带的总体提升是$\sim4$，在温度高于$10^{6}$ K和过密度$δ\gtrsim100$时急剧下降。除了发射率的提高之外，共振散射的贡献还改变了谱线的相对强度，因此在考虑高分辨率光谱的线比诊断或低分辨率光谱的红移确定时应该考虑到这一点。通过比较WHIM在X射线吸收和发射方面的特征，可以在未来的X射线飞行任务中区分真正的小超密度扩散气体和小填充因子的致密团块。
英文摘要：
We revisit calculations of the X-ray emission from warm-hot intergalactic medium (WHIM) with particular focus on contribution from the resonantly scattered cosmic X-ray background (CXB). If the significant part of the CXB emission is resolved into point sources, the properties of the WHIM along the line of sight are recorded in the absorption lines in the stacked spectrum of resolved sources and in the emission lines in the remaining diffuse signal. For the strongest resonant lines, this implies a factor of $\sim30$ boost in emissivity compared to the intrinsic emissivity over the major part of the density-temperature parameter space region relevant for WHIM. The overall boost for the 0.5-1 keV band is $\sim4$, declining steeply at temperatures above $10^{6}$ K and over-densities $δ\gtrsim100$. In addition to the emissivity boost, contribution of the resonant scattering changes relative intensities of the lines, so it should be taken into account when line-ratio-diagnostics from high resolution spectra or redshift determination from low resolution spectra are considered. Comparison between WHIM signatures in X-ray absorption and emission should allow differentiating truly diffuse gas of small overdensity from denser clumps having small filling factor by future X-ray missions.
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