[论文解读] Dark Energy Survey Year 1 Results: Multi-Probe Methodology and Simulated Likelihood Analyses

E. Krause, T. F. Eifler+84 more|arXiv (Cornell University)|Jun 28, 2017

Galaxies: Formation, Evolution, Phenomena参考文献 1被引用 126

一句话总结

本论文提出方法论、两条独立的似然流水线以及 DES Y1 3x2pt 分析的协方差验证，结合宇宙剪切、星系-星系透镜和星系聚类，包含稳健的尺度截断和系统误差建模。

ABSTRACT

We present the methodology for and detail the implementation of the Dark Energy Survey (DES) 3x2pt DES Year 1 (Y1) analysis, which combines configuration-space two-point statistics from three different cosmological probes: cosmic shear, galaxy-galaxy lensing, and galaxy clustering, using data from the first year of DES observations. We have developed two independent modeling pipelines and describe the code validation process. We derive expressions for analytical real-space multi-probe covariances, and describe their validation with numerical simulations. We stress-test the inference pipelines in simulated likelihood analyses that vary 6-7 cosmology parameters plus 20 nuisance parameters and precisely resemble the analysis to be presented in the DES 3x2pt analysis paper, using a variety of simulated input data vectors with varying assumptions. We find that any disagreement between pipelines leads to changes in assigned likelihood $Δχ^2 \le 0.045$ with respect to the statistical error of the DES Y1 data vector. We also find that angular binning and survey mask do not impact our analytic covariance at a significant level. We determine lower bounds on scales used for analysis of galaxy clustering (8 Mpc$~h^{-1}$) and galaxy-galaxy lensing (12 Mpc$~h^{-1}$) such that the impact of modeling uncertainties in the non-linear regime is well below statistical errors, and show that our analysis choices are robust against a variety of systematics. These tests demonstrate that we have a robust analysis pipeline that yields unbiased cosmological parameter inferences for the flagship 3x2pt DES Y1 analysis. We emphasize that the level of independent code development and subsequent code comparison as demonstrated in this paper is necessary to produce credible constraints from increasingly complex multi-probe analyses of current data.

研究动机与目标

• 为 DES Y1 多探针（3x2pt）宇宙学提供并验证似然框架的动机与有效性。
• 开发并比较两个独立的建模流水线，以确保推断的稳健性。
• 推导并验证解析的实空间多探针协方差矩阵。
• 评估尺度截断和系统误差对宇宙学参数恢复的影响。
• 展示推断对各种系统效应的鲁棒性。

提出的方法

• 使用 Limber 近似积分和非线性物质幂谱，构建三个探针角二点函数的基线理论模型。
• 实现两条独立的流水线（基于 CosmoSIS 和基于 CosmoLike）以计算数据向量和协方差。
• 推导解析的实空间多探针协方差并与仿真进行验证。
• 通过包含 6–7 个宇宙学参数和约 ~20 个边缘参数的模拟似然分析，对推断进行压力测试。
• 使用光学红移、星系偏倚、剪切标定和固有对齐等系统误差，并给出相应的先验和尺度截断。
• 采用跨 tomographic bin 的联合 3x2pt 数据向量，包含 xi_plus、xi_minus、gamma_t 和 w。

实验结果

研究问题

• RQ1 Can a dual independent modeling pipeline yield consistent cosmological inferences for DES Y1 3x2pt data?
• RQ2 How do analytic covariances perform relative to numerical simulations in a multi-probe setup?
• RQ3 What scale-cuts are required to ensure non-linear modeling uncertainties are subdominant to statistical errors?
• RQ4 How robust are DES Y1 inferences to priors and nuisance parameter modeling of photo-z, bias, shear calibration, and intrinsic alignments?
• RQ5 What is the gain in information from combining cosmic shear, galaxy–galaxy lensing, and galaxy clustering compared to individual probes?

主要发现

• Disagreement between the two pipelines yields Δχ2 ≤ 0.045 relative to the DES Y1 statistical error.
• Angular binning and survey mask do not significantly affect the analytic covariance.
• Lower scale cuts of ~8 Mpc/h for clustering and ~12 Mpc/h for galaxy–galaxy lensing keep non-linear modeling uncertainties below statistical errors.
• The joint 3x2pt analysis yields robust, unbiased cosmological parameter inferences for the DES Y1 analysis.
• Independent code development and cross-checks are essential for credible multi-probe cosmological constraints.