欧几里得：为3×2pt功率谱对暗能量约束优化视差红移分箱
Euclid: Optimising tomographic redshift binning for 3$\times$2pt power spectrum constraints on dark energy
AI总结：
本研究通过模拟探索欧几里得任务3×2pt分析中最佳的视差红移分箱策略，发现等量星系分箱对暗能量参数约束最优，但宇宙shear部分对分箱方法不敏感，且信息增益在7-8个分箱后趋于饱和。
摘要：
我们提出一种基于模拟的方法，以探索欧几里得任务3×2pt分析中最佳的视差红移分箱策略，重点在于其首个主要数据释放（DR1）的预期配置。为此，我们1）模拟欧几里得类观测，生成多个3×2pt场的模拟切片目录；2）对给定的视差分箱配置测量3×2pt伪Cl功率谱，并推导其对标准暗能量方程状态参数(w0, wa)的约束。在包含高斯分布的光谱红移不确定性及形状噪声的ΛCDM宇宙学背景下，我们发现等量星系分箱对完整3×2pt信号或角聚类部分的约束最佳。对于宇宙 shear 部分，最佳(w0, wa)约束通过在fiducial共动距离上等间距分箱实现。然而，与替代分箱选择相比，优势仅在1σ(w0, wa)轮廓大小上为几个百分比，我们得出结论，宇宙 shear 对分箱方法相对不敏感。我们发现，对于任何3×2pt成分，提取的(w0, wa)信息增益在7-8个分箱以上开始饱和。任何更多的分箱带来的边际增益可能受限于实际测量中的额外不确定性以及协方差矩阵的精度需求。最后，我们考虑5%的灾难性光谱红移异常污染，发现若不加以抑制，10个等量分箱的3×2pt信号偏差会导致暗能量约束与ΛCDM宇宙学模型不一致。
英文摘要：
We present a simulation-based method to explore the optimum tomographic redshift binning strategy for 3x2pt analyses with Euclid, focusing on the expected configuration of its first major data release (DR1). To do this, we 1) simulate a Euclid-like observation and generate mock shear catalogues from multiple realisations of the 3x2pt fields on the sky, and 2) measure the 3x2pt Pseudo-Cl power spectra for a given tomographic configuration and derive the constraints that they place on the standard dark energy equation of state parameters (w0, wa). For a simulation including Gaussian-distributed photometric redshift uncertainty and shape noise under a LambdaCDM cosmology, we find that bins equipopulated with galaxies yield the best constraints on (w0, wa) for an analysis of the full 3x2pt signal, or the angular clustering component only. For the cosmic shear component, the optimum (w0, wa) constraints are achieved by bins equally spaced in fiducial comoving distance. However, the advantage with respect to alternative binning choices is only a few percent in the size of the $1\,σ\,$(w0, wa) contour, and we conclude that the cosmic shear is relatively insensitive to the binning methodology. We find that the information gain extracted on (w0, wa) for any 3x2pt component starts to saturate at $\gtrsim$ 7-8 bins. Any marginal gains resulting from a greater number of bins is likely to be limited by additional uncertainties present in a real measurement, and the increasing demand for accuracy of the covariance matrix. Finally, we consider a 5% contamination from catastrophic photometric redshift outliers and find that, if these errors are not mitigated in the analysis, the bias induced in the 3x2pt signal for 10 equipopulated bins results in dark energy constraints that are inconsistent with the fiducial LambdaCDM cosmology at $>5\,σ$.
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