We investigate the dispersion measure(DM) and scattering of FRBs by the intergalactic-medium(IGM), foreground and host halos, using cosmological hydrodynamical simulation. We find that the median DM caused by foreground halos is around 30\% of that caused by the IGM, but has a much larger variance. The DM induced by hosts deviates from a log-normal distribution, but exhibits an extended distribution in the range of $1-3000 \ {\rm{pc\, cm^{-3}}}$ with a median value $\sim 100 \ {\rm{pc\, cm^{-3}}}$. Then we produce mock FRB sources, assuming a uniform distribution in the range $z\sim 0-0.82$, to consider the propagation effect of IGM, foreground and host halos on FRB signals simultaneously. The DM distribution of mock sources agrees well with the observation. The fitted DM-redshift relation of the mock sources can provide a rough estimation of the redshifts of observed events with errors $\delta z \lesssim 0.15$. The distribution of mock sources in the DM-scattering time($\tau$) space can also match the observation, assuming a Kolmogorov turbulence model with the inner and outer scale is 1000 km to 1 AU, and 0.2-10 pc respectively. Finally, we estimate the relative importance of these medium on DM and $\tau$ in our models. The IGM and host halos are the primary and secondary sources to the extragalactic DM, $\rm{DM_{exg}}$. Meanwhile, the contribution from foreground halos increases as $\rm{DM_{exg}}$ increases. The host and foreground halos may be the most important medium for scattering. Statistically, the latter may dominate the scattering of events with $\rm{DM_{exg}} \gtrsim 200 \ {\rm{pc\, cm^{-3}}}$.

中文翻译：

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快速射电暴的色散测量和散射：来自星系际介质、前景晕和宿主的贡献

我们使用宇宙学流体动力学模拟研究了星系间介质 (IGM)、前景和宿主晕对 FRB 的色散测量 (DM) 和散射。我们发现由前景晕引起的中值 DM 大约是由 IGM 引起的 DM 的 30%，但具有更大的方差。宿主引起的 DM 偏离对数正态分布，但表现出在 $1-3000 \ {\rm{pc\, cm^{-3}}}$ 范围内的扩展分布，中值为 $\sim 100 \ {\rm{pc\, cm^{-3}}}$。然后我们生成模拟 FRB 源，假设在 $z\sim 0-0.82$ 范围内均匀分布，以同时考虑 IGM、前景和主晕对 FRB 信号的传播影响。模拟源的 DM 分布与观察结果非常吻合。模拟源的拟合 DM-红移关系可以粗略估计观测到的事件的红移，误差为 $\delta z \lesssim 0.15$。DM-scattering time($\tau$)空间中模拟源的分布也可以与观测相匹配，假设Kolmogorov湍流模型的内外尺度分别为1000 km到1 AU和0.2-10 pc。最后，我们在我们的模型中估计了这些介质对 DM 和 $\tau$ 的相对重要性。IGM 和宿主晕是河外 DM $\rm{DM_{exg}}$ 的主要和次要来源。同时，前景光晕的贡献随着 $\rm{DM_{exg}}$ 的增加而增加。主光晕和前景光晕可能是最重要的散射介质。从统计上看，后者可能以 $\rm{DM_{exg}} \gtrsim 200 \ {\rm{pc\,