Testing the cold dark matter paradigm with dwarf galaxies and stellar streams in Gaia and LSST

星系包含大量不可见暗物质的第一个证据是在50多年前被发现的。从那时起，我们了解到暗物质的丰度是宇宙中普通物质的五倍多，它是星系演化的关键驱动力之一，因为包括银河系在内的所有星系都嵌入了巨大的暗物质晕中。然而，我们对暗物质粒子的性质及其在银河系和其他星系中的分布仍然知之甚少。此外，虽然目前基于冷暗物质的宇宙学范式(Lambda CDM)在复制大量观测数据方面非常成功，但这个模型在小尺度上的预测仍然测试得很差。我的研究目标是利用我们的银河系邻居，如围绕银河系运行的矮小星系和恒星流(被银河系潮汐破坏的卫星产生的恒星流)来测试Lambda CDM，并了解更多关于暗物质的知识。特别是，我计划使用盖亚卫星和其他大型天空测量数据，如LSST，来发现和描述恒星流。对恒星流的搜索和分析将有助于我了解银河系形成的过去历史。恒星流的位置和速度的模型将告诉我我们银河系内的质量分布，特别是暗物质的分布；对恒星流内恒星密度分布的分析将使我能够探测到由小的暗物质晕产生的微小引力扰动。我还计划开发新的方法，在盖亚的数据中搜索围绕银河系运行的矮星系。这将使我能够探测到质量比以前更低、距离太阳更近的星系，从而能够在小范围内研究暗物质并寻找暗物质湮灭信号。最后，我还计划解决一个问题，这个问题对于在大型星空成像调查中搜索矮小星系和恒星流极其重要：恒星与星系的分离。随着许多深部成像测量的进行和LSST测量的临近，我们区分暗恒星和暗星系的能力正在成为研究银河系周围暗结构的主要限制因素。

The first evidence that galaxies contain large amount of invisible dark matter has been revealed more than 50 years ago. Since then we learned that dark matter is more than five times more abundant than ordinary matter in the universe and that it is one of the key drivers of galaxy evolution, as all the galaxies including the Milky Way are embedded inside large dark matter halos. However, we still do not know much about the nature of dark matter particles and their distribution in the Milky Way and other galaxies. Also while the current cosmological paradigm based on cold dark matter (Lambda CDM) is very successful in reproducing a vast range of observations, the predictions of this model on small scales remain very poorly tested.The goal of my research is to use our galactic neighbourhood, such as dwarf galaxies, orbiting around the Milky Way and stellar streams (streams of stars produced by satellites tidally disrupted by the Milky Way) to test Lambda CDM and learn more about dark matter. In particular I plan to use data from the Gaia satellite and other large surveys of the sky such as LSST to find and characterize stellar streams. The search and analysis of stellar streams will help me understand the past history of the Milky Way formation. The modelling of positions and velocities of stellar streams will tell me about the distribution of mass inside our Galaxy and in particular the distribution of dark matter; the analysis of the stellar density distribution inside stellar streams will allow me to detect small gravitational perturbations produced by small dark matter halos. I also plan to develop new methods to search for dwarf galaxies orbiting the Milky Way in the Gaia data. This should allow me to detect galaxies of even lower mass than before and located even closer to the Sun, thus enabling studies of the dark matter at small scales and searches for dark matter annihilation signal. Finally, I also plan to tackle a problem that is extremely important for the searches of dwarf galaxies and stellar streams in large imaging surveys of the sky: star-galaxy separation. With many deep imaging surveys ongoing and LSST survey around the corner, our ability of separating faint stars from faint galaxies is becoming the main limiting factor for the studies of faint structures around the Milky Way.