arXiv 1902.000442019-02astro-ph.CO

欧几里得制备IV。未探测星系对弱透镜剪切测量的影响

Euclid Preparation IV. Impact of undetected galaxies on weak-lensing shear measurements

Euclid Collaboration, N. Martinet, T. Schrabback, H. Hoekstra, M. Tewes, R. Herbonnet, P. Schneider, B. Hernandez-Martin, A. N. Taylor, J. Brinchmann, C. S. Car… 展开作者

Euclid Collaboration, N. Martinet, T. Schrabback, H. Hoekstra, M. Tewes, R. Herbonnet, P. Schneider, B. Hernandez-Martin, A. N. Taylor, J. Brinchmann, C. S. Carvalho, M. Castellano, G. Congedo, B. R. Gillis, E. Jullo, M. Kümmel, S. Ligori, P. B. Lilje, C. Padilla, D. Paris, J. A. Peacock, S. Pilo, A. Pujol, D. Scott, R. Toledo-Moreo

备注：: Version published in A&A
发表信息：: A&A 627, A59 (2019)
DOI：: 10.1051/0004-6361/201935187

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摘要：

在现代弱透镜测量中，校正剪切中的残余系统偏差的常用方法是使用模拟来校准形状测量算法。这些模拟必须充分捕捉观察的复杂性，以避免引入任何额外的偏差。在本文中，我们研究的重要性，暗星系的观测探测极限以下的调查。我们模拟简化的欧几里德VIS图像，包括和排除这个微弱的人口，并测量两组模拟之间的乘法剪切偏差的变化。我们用三种不同的算法测量剪切力：基于矩的方法、模型拟合和机器学习。我们发现，对于所有的方法，一个空间均匀的随机分布的微弱星系介绍了几次$10^{-3}$的顺序剪切乘法偏差。这个值增加到$10^{-2}$的数量级时，包括集群的微弱星系，在哈勃太空望远镜超深场测量。研究发现，由于视线上较亮的星系而导致的微弱背景星系的放大对乘法偏差的影响可以忽略不计。我们的结论是，未检测到的星系必须包括在校准模拟与适当的聚类性能下降到28等，以达到一个残留的不确定性的乘法剪切偏置校准的几倍$10^{-4}$，符合$2\times10^{-3}$总精度预算所需的科学目标的欧几里得调查。我们提出了两种互补的方法，包括微弱的星系聚类的校准模拟。

英文摘要：

In modern weak-lensing surveys, the common approach to correct for residual systematic biases in the shear is to calibrate shape measurement algorithms using simulations. These simulations must fully capture the complexity of the observations to avoid introducing any additional bias. In this paper we study the importance of faint galaxies below the observational detection limit of a survey. We simulate simplified Euclid VIS images including and excluding this faint population, and measure the shift in the multiplicative shear bias between the two sets of simulations. We measure the shear with three different algorithms: a moment-based approach, model fitting, and machine learning. We find that for all methods, a spatially uniform random distribution of faint galaxies introduces a shear multiplicative bias of the order of a few times $10^{-3}$. This value increases to the order of $10^{-2}$ when including the clustering of the faint galaxies, as measured in the Hubble Space Telescope Ultra-Deep Field. The magnification of the faint background galaxies due to the brighter galaxies along the line of sight is found to have a negligible impact on the multiplicative bias. We conclude that the undetected galaxies must be included in the calibration simulations with proper clustering properties down to magnitude 28 in order to reach a residual uncertainty on the multiplicative shear bias calibration of a few times $10^{-4}$, in line with the $2\times10^{-3}$ total accuracy budget required by the scientific objectives of the Euclid survey. We propose two complementary methods for including faint galaxy clustering in the calibration simulations.

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