A multi-probe strategy to pin down the nature of gravity and dark energy

确定引力和暗能量本质的多探针策略

• 批准号: ST/L00285X/1
• 负责人: Benjamin Joachimi
• 金额: $ 27.8万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2015
• 资助国家: 英国
• 起止时间: 2015 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FL00285X%2F1
• 关键词: multi; probe; strategy; pin; down

The Nobel Prize in Physics 2011 was awarded to the puzzling discovery that the Universe is not only expanding, but doing so with ever increasing speed, whereas in the standard picture of cosmology it was expected to slow down. This acceleration could either be due to a new exotic matter component called dark energy which is repellent and would form the major ingredient of the cosmos. Alternatively, the laws of gravity as predicted by Einstein's general relativity may not be quite correct on cosmological scales and need to be modified.One of the best ways to pin down the properties of dark energy and test general relativity on cosmological scales is to study the large-scale distribution of matter in the Universe and its evolution, together with its gravitational interactions. In a novel approach to probe this distribution, I am going to simultaneously analyse the positions, the velocities, and the shapes of millions of distant galaxies.The clustering of galaxies in space provides a picture of the underlying matter distribution since galaxies trace the matter density. However, the picture is biased because galaxies preferentially reside in high-density regions, and this galaxy bias limits the cosmological information that can be extracted from clustering.Using galaxy velocity measurements, one can infer the coherent motions of galaxies due to the large-scale gravitational forces via so-called redshift-space distortions, causing apparent overdensities of galaxies when these are attracted by a large mass. This effect needs to be disentangled from the actual clustering of galaxies, which is again hindered by galaxy bias, so that the power of redshift-space distortions alone to constrain cosmological parameters is limited as well.General relativity predicts that large masses can deflect light rays similar to a magnifying glass - therefore the term gravitational lensing was coined for this effect. The images of distant galaxies are distorted by the gravitational lensing of the large-scale structure of the Universe between these galaxies and Earth. These 'cosmic shear' distortions directly map the intervening matter distribution, without any dependence on galaxy bias. In addition, cosmic shear also probes the geometry of the cosmos as it depends on the distances between the light sources, the lenses, and the observer. This potentially very powerful cosmological probe is plagued by intrinsic alignments of galaxy shapes which mimic the distortions characteristic of cosmic shear and hence limit the accuracy of cosmological measurements.The key to overcome the limitations of the three probes is to analyse them jointly and also include their cross-correlations into the analysis. This will lift degeneracies between parameters as for instance caused by the galaxy bias, and calibrate systematic effects such as the intrinsic alignment contamination of cosmic shear. With this technique I will obtain significantly better constraints on dark energy and the laws of gravity than from any individual probe, and the results will additionally be much less susceptible to systematic errors.This approach requires an imaging survey with excellent image quality to measure the shapes of faint and small galaxy images which overlaps with a redshift survey that allows for the accurate measurement of galaxy distances which are needed to measure clustering and redshift-space distortions. The research team that I am going to lead has access to a unique pair of such surveys. The quality and size of the joint data set is so good that I can target different types of galaxies at the same time and thus apply even more advanced techniques to eliminate systematic effects from the measurements. The joint scientific analysis will therefore yield unprecedented precision and accuracy on the properties of dark energy and the nature of gravity.

2011 年诺贝尔物理学奖授予了一项令人费解的发现：宇宙不仅在膨胀，而且膨胀速度不断加快，而在宇宙学的标准图景中，宇宙的速度预计会减慢。这种加速可能是由于一种称为暗能量的新奇特物质成分造成的，它具有排斥性，将构成宇宙的主要成分。或者，爱因斯坦广义相对论所预测的引力定律在宇宙学尺度上可能不太正确，需要修改。在宇宙学尺度上确定暗能量的性质并测试广义相对论的最佳方法之一是研究宇宙中物质的大规模分布及其演化，及其引力相互作用。在探索这种分布的新颖方法中，我将同时分析数百万个遥远星系的位置、速度和形状。空间中星系的聚集提供了底层物质分布的图片，因为星系追踪物质密度。然而，这张图是有偏差的，因为星系优先居住在高密度区域，这种星系偏差限制了可以从聚类中提取的宇宙学信息。利用星系速度测量，我们可以推断出星系由于大尺度的相干运动。通过所谓的红移空间扭曲产生的引力，当星系被大质量吸引时，会导致星系明显密度过大。这种效应需要与实际的星系团分开，而星系团又受到星系偏差的阻碍，因此红移空间扭曲单独限制宇宙学参数的力量也很有限。广义相对论预测大质量可以使光线偏转类似于放大镜 - 因此引力透镜这个术语就是为了这种效果而创造的。遥远星系的图像因这些星系与地球之间宇宙大尺度结构的引力透镜而扭曲。这些“宇宙剪切”扭曲直接映射了介入的物质分布，而不依赖于星系偏差。此外，宇宙剪切还可以探测宇宙的几何形状，因为它取决于光源、透镜和观察者之间的距离。这种潜在非常强大的宇宙学探测器受到星系形状固有排列的困扰，这些排列模仿了宇宙剪切的扭曲特征，因此限制了宇宙学测量的准确性。克服这三个探测器局限性的关键是对它们进行联合分析，并包括它们的交叉相关分析。这将消除例如由星系偏差引起的参数之间的简并，并校准系统效应，例如宇宙剪切的内在对准污染。通过这种技术，我将获得比任何单个探测器更好的对暗能量和万有引力定律的约束，并且结果将更不容易受到系统误差的影响。这种方法需要具有出色图像质量的成像测量来测量形状微弱和小的星系图像，与红移勘测重叠，可以精确测量星系距离，这是测量聚类和红移空间扭曲所需的。我将领导的研究团队可以获得一对独特的此类调查。联合数据集的质量和大小非常好，以至于我可以同时瞄准不同类型的星系，从而应用更先进的技术来消除测量中的系统效应。因此，联合科学分析将对暗能量的特性和重力的本质产生前所未有的精确度和准确度。

项目成果

CFHTLenS revisited: assessing concordance with Planck including astrophysical systematics

重新审视 CFHTLenS：评估与普朗克的一致性，包括天体物理系统学

• DOI: 10.1093/mnras/stw2665
• 发表时间: 2016-01-21
• 期刊: Monthly Notices of the Royal Astronomical Society
• 影响因子: 4.8
• 作者: S. Joudaki;C. Blake;C. Heymans;A. Choi;J. Harnois;H. Hildebr;t;t;B. Joachimi;Andrew Johnson
• 通讯作者: Andrew Johnson

KiDS-i-800: comparing weak gravitational lensing measurements from same-sky surveys

KiDS-i-800：比较同一天空观测的弱引力透镜测量

• DOI: http://dx.10.1093/mnras/sty859
• 发表时间: 2018
• 期刊: Monthly Notices of the Royal Astronomical Society
• 影响因子: 4.8
• 作者: Amon A

Multiwavelength scaling relations in galaxy groups: a detailed comparison of GAMA and KiDS observations to BAHAMAS simulations

星系群中的多波长标度关系：GAMA 和 KiDS 观测与 BAHAMAS 模拟的详细比较

• DOI: http://dx.10.1093/mnras/sty2017
• 发表时间: 2018
• 期刊: Monthly Notices of the Royal Astronomical Society
• 影响因子: 4.8
• 作者: Jakobs A

Dependence of GAMA galaxy halo masses on the cosmic web environment from 100 deg 2 of KiDS weak lensing data

来自 KiDS 100 deg 2 弱透镜数据的 GAMA 星系晕质量对宇宙网环境的依赖性

• DOI: http://dx.10.1093/mnras/stw1602
• 发表时间: 2016
• 期刊: Monthly Notices of the Royal Astronomical Society
• 影响因子: 4.8
• 作者: Brouwer M

Studying galaxy troughs and ridges using Weak Gravitational Lensing with the Kilo-Degree Survey

使用弱引力透镜和千度巡天研究星系槽和脊

• DOI: http://dx.10.48550/arxiv.1805.00562
• 发表时间: 2018
• 作者: Brouwer M