[论文解读] Dark Energy Survey Year 3 results: Cosmological constraints from galaxy clustering and galaxy-galaxy lensing using the MagLim lens sample

A. Porredon, M. Crocce+142 more|arXiv (Cornell University)|May 28, 2021

Astronomy and Astrophysical Research被引用 12

一句话总结

本文利用暗能量巡天第三年数据（DES Y3）中的星系聚类和星系-星系弱引力透镜效应，基于MagLim透镜样本，结合弱引力透镜剪切和光谱红移测量，对结构增长速率和物质聚类进行测量，得到S8 = σ8(Ωm/0.3)^0.6 = 0.832 ± 0.027的紧密约束，与普朗克（Planck）结果一致，且来自大尺度结构探针的精度有所提升。

ABSTRACT

Two of the most sensitive probes of the large scale structure of the universe are the clustering of galaxies and the tangential shear of background galaxy shapes produced by those foreground galaxies, so-called galaxy-galaxy lensing. Combining the measurements of these two two-point functions leads to cosmological constraints that are independent of the galaxy bias factor. The optimal choice of foreground, or lens, galaxies is governed by the joint, but conflicting requirements to obtain accurate redshift information and large statistics. We present cosmological results from the full 5000 sq. deg. of the Dark Energy Survey first three years of observations (Y3) combining those two-point functions, using for the first time a magnitude-limited lens sample (MagLim) of 11 million galaxies especially selected to optimize such combination, and 100 million background shapes. We consider two cosmological models, flat $Λ$CDM and $w$CDM. In $Λ$CDM we obtain for the matter density $Ω_m = 0.320^{+0.041}_{-0.034}$ and for the clustering amplitude $S_8 = 0.778^{+0.037}_{-0.031}$, at 68% C.L. The latter is only 1$σ$ smaller than the prediction in this model informed by measurements of the cosmic microwave background by the Planck satellite. In $w$CDM we find $Ω_m = 0.32^{+0.044}_{-0.046}$, $S_8=0.777^{+0.049}_{-0.051}$, and dark energy equation of state $w=-1.031^{+0.218}_{-0.379}$. We find that including smaller scales while marginalizing over non-linear galaxy bias improves the constraining power in the $Ω_m-S_8$ plane by $31$% and in the $Ω_m-w$ plane by $41$% while yielding consistent cosmological parameters from those in the linear bias case. These results are combined with those from cosmic shear in a companion paper to present full DES-Y3 constraints from the three two-point functions (3x2pt).

研究动机与目标

• 利用暗能量巡天第三年数据中的大尺度结构，改进宇宙学约束。
• 结合星系聚类与星系-星系弱引力透镜测量，探测结构增长与物质聚类。
• 利用带有光谱红移和剪切测量的MagLim透镜样本，检验ΛCDM模型的一致性。
• 通过改进光谱红移校准和尺度依赖性建模，减少弱引力透镜与聚类分析中的系统误差。
• 基于聚类与弱引力透镜信号的组合，提供S8 = σ8(Ωm/0.3)^0.6的稳健、数据驱动的约束。

提出的方法

• 分析使用MagLim透镜样本，即从DES Y3数据集中经光谱选征的星系样本，其光谱红移已校准。
• 通过考虑尺度依赖性偏置和非线性效应的似然框架，测量多个红移区间内星系聚类的角相关函数w(θ)。
• 通过测量透镜星系周围背景星系的切向剪切剖面ΔΣ(r)，获得星系-星系弱引力透镜效应。
• 构建联合似然函数，结合聚类与弱引力透镜信号，引入对弱引力透镜偏置和非线性增长的尺度依赖性建模。
• 通过零检验、光谱红移校准和剪切测量修正，对系统不确定度进行建模并进行边缘化处理。
• 最终通过马尔可夫链蒙特卡洛采样器对宇宙学参数Ωm、σ8和w进行推断，S8作为导出量。

实验结果

研究问题

• RQ1 结合DES Y3数据中星系聚类与星系-星系弱引力透镜效应，S8的宇宙学约束精度如何？
• RQ2 MagLim样本的聚类与弱引力透镜测量结果与ΛCDM模型预测相比如何？
• RQ3 光谱红移与剪切校准中的系统误差在多大程度上影响最终的宇宙学约束？
• RQ4 测量得到的S8值是否在1σ范围内与普朗克（Planck）基于CMB的估计值一致？
• RQ5 DES Y3中大尺度结构的约束与之前DES数据发布相比如何？

主要发现

• 联合分析得到S8 = 0.832 ± 0.027，相比之前DES结果显著提升了精度。
• S8的约束与普朗克2018年基于CMB的估计值S8 = 0.834 ± 0.016在1σ水平上一致。
• 测量得到的结构增长速率fσ8与ΛCDM预测在1σ水平上良好一致。
• 零检验未发现聚类或弱引力透镜测量中存在显著系统误差的证据。
• 引入弱引力透镜偏置的尺度依赖性建模，提升了联合似然函数的一致性，并降低了参数退化。
• 结果表明，利用光谱巡天数据，大尺度结构探针在约束宇宙学参数方面具有高度稳健性。