CFHTLenS弱透镜剪切数据中的约束乘性偏差
Constraining Multiplicative Bias in CFHTLenS Weak Lensing Shear Data
摘要：
最近的一些宇宙学分析发现，来自加拿大-法国-夏威夷望远镜透镜巡天（CFHTLenS）数据的约束与来自其他数据集（如普朗克宇宙微波背景（CMB）温度各向异性）的约束之间存在紧张关系。类似地，CFHTLenS数据与普朗克CMB透镜数据的直接互相关产生了与基于普朗克或WMAP导出的宇宙学参数的预期相比非常低的振幅（Liu & Hill 2015）。这些结果的一个潜在解释是影响CFHTLenS星系形状测量的乘法偏差，从中推断出剪切。CFHTLenS管道中使用模拟来校准此类偏差，但迄今为止尚未提出数据驱动的约束。在本文中，我们将CFHTLenS星系密度图与CFHTLenS剪切图和普朗克CMB透镜图进行交叉关联，以校准CFHTLenS中的额外乘法剪切偏差（m）（超出已经应用于CFHTLenS星系剪切的乘法校正），遵循Vallinotto（2012）和Das等人建议的方法。我们分析了三个星等有限的星系样本，发现使用最深的样本（i<24）的2-4sigma证据m<1，而其他的则与m=1一致（无偏差）。这与暗星系的形状最容易受到测量偏差的影响的预期相匹配。我们的结果m基本上是独立的假设宇宙学，只有弱敏感的假设星系的偏见。我们考虑三个星系的偏见模型，发现在所有情况下，最适合的乘法剪切偏置小于统一。m~0.9的值足以使从CFHTLenS剪切两点统计推断的密度波动幅度与从普朗克CMB温度数据推断的密度波动幅度一致。这种情况与我们的结果是一致的。
英文摘要：
Several recent cosmological analyses have found tension between constraints derived from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) data and those derived from other data sets, such as the Planck cosmic microwave background (CMB) temperature anisotropies. Similarly, a direct cross-correlation of the CFHTLenS data with Planck CMB lensing data yielded an anomalously low amplitude compared to expectations based on Planck or WMAP-derived cosmological parameters (Liu & Hill 2015). One potential explanation for these results is a multiplicative bias afflicting the CFHTLenS galaxy shape measurements, from which shears are inferred. Simulations are used in the CFHTLenS pipeline to calibrate such biases, but no data-driven constraints have been presented to date. In this paper, we cross-correlate CFHTLenS galaxy density maps with CFHTLenS shear maps and Planck CMB lensing maps to calibrate an additional multiplicative shear bias (m) in CFHTLenS (beyond the multiplicative correction that has already been applied to the CFHTLenS galaxy shears), following methods suggested by Vallinotto (2012) and Das et al. (2013). We analyze three magnitude-limited galaxy samples, finding 2-4sigma evidence for m<1 using the deepest sample (i<24), while the others are consistent with m=1 (no bias). This matches the expectation that the shapes of faint galaxies are the most prone to measurement biases. Our results for m are essentially independent of the assumed cosmology, and only weakly sensitive to assumptions about the galaxy bias. We consider three galaxy bias models, finding in all cases that the best-fit multiplicative shear bias is less than unity. A value of m~0.9 would suffice to reconcile the amplitude of density fluctuations inferred from the CFHTLenS shear two-point statistics with that inferred from Planck CMB temperature data. This scenario is consistent with our results.
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