Detection and characterisation of dark-matter halos by gravitational shear and flexion; constraints on the non-linear cosmic structure growth

引力透镜是研究宇宙暗结构及其在宇宙学时期的增长的最强大的工具之一。在过去的几年里，宇宙剪切的精确测量已经惊人地迅速发展成为支撑宇宙标准模型的支柱之一。切变跟踪重力潮汐场，即引力势的二阶导数。重要的信息也必须包含在它的第三个衍生品中，这些衍生品可以方便地组合在一起，形成两个分量的弯曲。尽管弯曲的阶数更高，但与剪切相比，弯曲具有类似或更好的信噪比特性。它对物质分布中较小尺度的敏感性使其成为一种非常有趣和受欢迎的工具，用于探测暗物质晕并研究其内部组成，从而测试对清洁发展机制宇宙的一般性预测，这些预测仍然存在争议。我们继续研究用于测量弯曲的形状技术，消除了它的一些限制和问题，开发了一种新的、可靠的实施方案，并证明它现在已经达到了与替代剪切测量类似的可靠性。我们在这里建议继续这一计划，以系统地校准弯曲测量的形状，将弯曲测量应用于详细重建星系团，探测暗物质晕及其子结构，以及研究非线性宇宙结构增长。

Gravitational lensing is among the most powerful tools to study dark structures in the Universe and their growth over cosmological epochs. Over the past years, the precise measurement of cosmic shear has developed impressively quickly into one of the pillars supporting the cosmological standard model. The shear traces the gravitational tidal field, i.e. second derivatives of the gravitational potential. Important information must also be contained in its third derivatives, which can conveniently be combined to form the two-component flexion. Despite its higher order, flexion has comparable or superior signal-to-noise properties compared to the shear. Its sensitivity to smaller scales in the matter distribution makes it a highly interesting and welcome tool to detect dark-matter halos and to study their internal composition, and thus to test generic predictions of the CDM cosmogony which are still controversial. We have continued our study of the shapelet technique for measuring flexion, removed several of its limitations and problems, developed a new, reliable implementation and demonstrated that it has now reached similar reliability as alternative shear measurements. We here propose to continue this programme towards a systematic calibration of shapelet measurements of the flexion, applications of flexion measurements to the detailed reconstruction of galaxy clusters, the detection of dark-matter halos and their substructures, and the study of nonlinear cosmic structure growth.