[论文解读] Hyper Suprime-Cam Year 3 Results: Cosmology from Cosmic Shear Power Spectra

Roohi Dalal, Xiangchong Li+36 more|arXiv (Cornell University)|Apr 3, 2023

Galaxies: Formation, Evolution, Phenomena参考文献 179被引用 25

一句话总结

本论文利用 Hyper Suprime-Cam 第三年数据测量弱透镜宇宙剪切功率谱，推导 S8 约束，并测试对系统误差与建模选择的鲁棒性。

ABSTRACT

We measure weak lensing cosmic shear power spectra from the three-year galaxy shear catalog of the Hyper Suprime-Cam (HSC) Subaru Strategic Program imaging survey. The shear catalog covers $416 \ \mathrm{deg}^2$ of the northern sky, with a mean $i$-band seeing of 0.59 arcsec and an effective galaxy number density of 15 $\mathrm{arcmin}^{-2}$ within our adopted redshift range. With an $i$-band magnitude limit of 24.5 mag, and four tomographic redshift bins spanning $0.3 \leq z_{\mathrm{ph}} \leq 1.5$ based on photometric redshifts, we obtain a high-significance measurement of the cosmic shear power spectra, with a signal-to-noise ratio of approximately 26.4 in the multipole range $300<\ell<1800$. The accuracy of our power spectrum measurement is tested against realistic mock shear catalogs, and we use these catalogs to get a reliable measurement of the covariance of the power spectrum measurements. We use a robust blinding procedure to avoid confirmation bias, and model various uncertainties and sources of bias in our analysis, including point spread function systematics, redshift distribution uncertainties, the intrinsic alignment of galaxies and the modeling of the matter power spectrum. For a flat $Λ$CDM model, we find $S_8 \equiv σ_8 (Ω_m/0.3)^{0.5} =0.776^{+0.032}_{-0.033}$, which is in excellent agreement with the constraints from the other HSC Year 3 cosmology analyses, as well as those from a number of other cosmic shear experiments. This result implies a $\sim$$2σ$-level tension with the Planck 2018 cosmology. We study the effect that various systematic errors and modeling choices could have on this value, and find that they can shift the best-fit value of $S_8$ by no more than $\sim$$0.5σ$, indicating that our result is robust to such systematics.

研究动机与目标

• 通过弱引力透镜实现精密宇宙学研究的动机与目标
• 通过分层（tomographic）分析提取宇宙剪切功率谱以打破参数退化
• 建模并减小系统性不确定性（点扩散函数 PSF、红移分布、固有排列、物质功率谱）
• 使用现实的模拟目录来校准协方差并通过盲测来避免偏差以实现验证

提出的方法

• 使用伪 C_ℓ 估计量在分层区间内计算宇宙剪切 E 模量功率谱以纠正不完整天空覆盖带来的影响
• 将剪切场分解为 E 模与 B 模以分离宇宙学信号并检验系统误差
• 使用图像仿真校准来纠正乘法和加性剪切偏差（包括选择偏差）
• 基于覆盖整张天空的 1404 个虚拟目录的广泛套件来估计协方差
• 实施两级盲法策略以防止确认偏差，在预设检验完成后再进行解盲
• 建模并对系统误差进行外推与边际化，如 PSF 残差、红shift 分布不确定性、固有对齐、非线性物质功率谱效应

实验结果

研究问题

• RQ1 使用 HSC 第三年数据在 0.3 ≤ z_ph ≤ 1.5 的分层区间中可达到的宇宙剪切信号水平是多少？
• RQ2 通过 HSC-Y3 宇宙剪切功率谱推断的平坦 ΛCDM 的 S8 参数是多少？与 Planck 以及其他调查相比如何？
• RQ3 对系统误差和建模选择（PSF、光斑红移、固有对齐、晕模型）而言，S8 的约束有多鲁棒？
• RQ4 交叉检验（空检验、B 模测量）是否指示任何显著的残留系统误差影响宇宙 interpretation？

主要发现

• 在平坦 ΛCDM 下 S8 = 0.776^{+0.032}_{-0.033}，与其他 HSC 分析和若干宇宙剪切调查结果一致
• 对 300 < ℓ < 1800 的信号到噪声比约为 26.4 的高显著性测量
• 未检测到显著的 B 模，表明测量中与 PSF 相关的系统误差可以忽略
• 系统误差和建模选择对 S8 的偏移不超过约 0.5σ，结果具有鲁棒性
• Planck 2018 宇宙学与 HSC-Y3 的 S8 约束存在约 2σ 的张力