The Epoch of Reionization (EoR) depends on the complex astrophysics governing the birth and evolution of the first galaxies and structures in the intergalactic medium. EoR models rely on cosmic microwave background (CMB) observations, and in particular the large-scale E-mode polarization power spectra (EE PS), to help constrain their highly uncertain parameters. However, rather than directly forward-modelling the EE PS, most EoR models are constrained using a summary statistic – the Thompson scattering optical depth, τ_e. Compressing CMB observations to τ_e requires adopting a basis set for the EoR history. The common choice is the unphysical, redshift-symmetric hyperbolic tangent (tanh) function, which differs in shape from physical EoR models based on hierarchical structure formation. Combining public EoR and CMB codes, 21cmfast and class, here we quantify how inference using the τ_e summary statistic impacts the resulting constraints on galaxy properties and EoR histories. Using the last Planck 2018 data release, we show that the marginalized constraints on the EoR history are more sensitive to the choice of the basis set (tanh versus physical model) than to the CMB likelihood statistic (τ_e versus PS). For example, EoR histories implied by the growth of structure show a small tail of partial reionization extending to higher redshifts. However, biases in inference using τ_e are negligible for the Planck 2018 data. Using EoR constraints from high-redshift observations including the quasar dark fraction, galaxy UV luminosity functions, and CMB EE PS, our physical model recovers |$\tau _\mathrm{ e} = 0.0569_{-0.0066}^{+0.0081}$|⁠.

中文翻译：

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来自 CMB 光学深度和 E 模式偏振功率谱的再电离推断

再电离时代 (EoR) 取决于控制星系间介质中第一个星系和结构的诞生和演化的复杂天体物理学。EoR 模型依赖于宇宙微波背景 (CMB) 观测，特别是大规模 E 模式偏振功率谱 (EE PS)，以帮助限制其高度不确定的参数。然而，大多数 EoR 模型不是直接对 EE PS 进行前向建模，而是使用汇总统计数据进行约束——汤普森散射光学深度，τ_e。将 CMB 观测值压缩到 τ_e 需要采用 EoR 历史的基组。常见的选择是非物理的、红移对称的双曲正切 (tanh) 函数，它的形状不同于基于层次结构形成的物理 EoR 模型。结合公共EoR和CMB代码，21cmfast和class，在这里，我们量化了使用 τ_e 汇总统计量的推断如何影响对星系属性和 EoR 历史产生的约束。使用最新的 Planck 2018 数据发布，我们表明 EoR 历史的边缘化约束对基组的选择（tanh 与物理模型）比对 CMB 似然统计（τ_e 与 PS）更敏感。例如，结构增长所暗示的 EoR 历史显示部分再电离的小尾巴延伸到更高的红移。然而，对于普朗克 2018 数据，使用 τ_e 进行推理的偏差可以忽略不计。使用来自高红移观测的 EoR 约束，包括类星体暗部分、星系 UV 光度函数和 CMB EE PS，我们的物理模型恢复 |$\tau _\mathrm{ e} = 0.0569_{-0.0066}^{+0.0081} $|⁠。