Advancing weak lensing and intrinsic galaxy alignment studies into the era of precision cosmology

宇宙学家现在可以在一个一致的框架中成功地解释宇宙的关键特征。然而，令人困惑的是，95%的宇宙成分似乎是以奇异的物质形式存在的，其性质仍然不清楚。人们发现，所有的天体，从星系到最大的结构，都比它们发出的光的总量更重。因此，大多数物质必须是未知的，不发光的类型，称为暗物质。此外，宇宙的几何结构和它的加速膨胀暗示了暗能量的存在。暗能量是一种更为奇特的成分，据推测占宇宙总能量预算的四分之三。引力透镜是揭示暗物质和暗能量本质的最有力的方法之一。爱因斯坦的相对论告诉我们，大质量的天体会使光线发生偏转，这样星系就可以像放大镜一样聚焦来自背景光源的光线--它就像一个引力透镜。类似于放大镜边缘附近的效果，遥远星系的图像会因视线沿着的物质对光的偏转而扭曲。通过测量数十亿个星系上的这些微小扭曲，我们可以探测这些星系和地球之间的物质分布，这反过来又取决于暗物质和暗能量的性质。这种用统计工具分析大量扭曲星系图像的方法被称为宇宙剪切。我的工作旨在利用在大部分天空中测量的宇宙剪切，高精度地确定宇宙黑暗组成部分的性质。我将把对星系图像失真的联合收割机测量与对星系位置、速度和距离的测量结合起来，进一步检验我们的引力理论在宇宙尺度上是否仍然正确。为了充分利用即将到来的宇宙学数据集，例如由欧洲欧几里得卫星（我参与了该卫星的设计）产生的数据集，我将开发和应用新的测量方法和分析工具，使我们能够获得迄今为止尚未使用的信息。获得高度精确的测量是至关重要的，但同样重要的是，它们不会受到所谓的“系统误差”的影响：与真实结果的未被发现的偏差，这将产生错误的答案，并导致我们得出错误的结论，就像用有错误刻度的天平测量质量一样。一个严重的系统误差是由星系引起的，这些星系由于其邻近物质施加的引力而变形和排列。这种效应被称为内在排列，它模拟了我们想要测量的宇宙切变中的扭曲，因此如果忽略它，就会产生很大的系统误差。然而，内禀星系排列不仅是一个讨厌的宇宙剪切测量，但可以为我们提供有价值的洞察星系的形成和演化的过程中，仍然在很大程度上是未知的，目前。为了提高我们对星系的认识和对宇宙剪切系统误差的控制，我将进行迄今为止最大的测量和分析内禀排列的努力，将在世界上最好的观测地点（夏威夷和加那利群岛，阿塔卡马沙漠和澳大利亚）用望远镜拍摄的大量数据集结合起来。通过联合研究宇宙剪切和内禀星系排列，我将能够从这些宇宙探测器中提取最大限度的信息，对黑暗和光明的宇宙产生独特的见解。

Cosmologists can nowadays successfully explain the key features of the Universe in a consistent framework. However it is puzzling that 95% of the cosmic ingredients appear to be in exotic forms of matter whose nature is still obscure. One finds that all astronomical objects, ranging from galaxies up to the largest structures, weigh more than the amount of light which they emit suggests. Hence, the majority of matter must be of a yet unknown, non-luminous type, termed dark matter. Furthermore, the geometry of the Universe and its accelerating expansion hint at the existence of dark energy, an even more exotic component that supposedly makes up three quarters of the total cosmic energy budget.Gravitational lensing is one of the most powerful ways of revealing the nature of dark matter and dark energy. Einstein's theory of relativity tells us that massive bodies deflect light such that a galaxy can focus the light from a background source like a magnifying glass - it acts as a gravitational lens. Similar to the effects close to the rim of a magnifying glass, the images of distant galaxies are distorted by the deflections of light by the matter along the line of sight. Measuring these tiny distortions on billions of galaxies, we can probe the distribution of matter between those galaxies and Earth, which in turn is determined by the properties of dark matter and dark energy. This method of analysing large numbers of distorted galaxy images with statistical tools is called cosmic shear.My work aims at determining the properties of the dark building blocks of the Universe with high precision, using cosmic shear measured on large fractions of the sky. I am going to combine measurements of galaxy image distortions with those of galaxy positions, velocities, and distances to go even further and test whether our theory of gravity is still correct on cosmological scales. To make the most of upcoming cosmological data sets, as e.g. produced by the European Euclid satellite whose design I have contributed to, I am going to develop and apply new measurement methods and analysis tools which allow us to access information that has remained unused hitherto.Obtaining highly accurate measurements is crucial, but it is equally important that they do not suffer from so-called "systematic errors": undetected deviations from the true result which would produce wrong answers and lead us to incorrect conclusions, much like measuring masses with a balance that has a faulty scale. A serious systematic error is caused by galaxies which are deformed and aligned by the gravitational pull exerted by matter in their neighbourhood. This effect, called intrinsic alignment, mimics the distortions that we want to measure in cosmic shear and thus causes strong systematic errors if ignored. However, intrinsic galaxy alignment is not only a nuisance to cosmic shear measurements, but can provide us with valuable insight into processes of galaxy formation and evolution which are still largely unknown at present. To improve both our understanding of galaxies and the control of cosmic shear systematic errors, I will undertake the hitherto biggest effort of measuring and analysing intrinsic alignments, combining large data sets taken with telescopes at the world's best observational sites on Hawaii and the Canary Islands, in the Atacama desert and Australia.By studying cosmic shear and intrinsic galaxy alignments jointly, I will be able to extract a maximum of information from each of these cosmological probes, yielding unique insights into both the dark and bright Universe.