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

星系中含有大量不可见暗物质的第一个证据是在50多年前发现的。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在大型暗物质晕中。然而，我们仍然不太了解暗物质粒子的性质及其在银河系和其他星系中的分布。同时，当前基于冷暗物质的宇宙学范式（Lambda CDM）在再现大范围的观测方面非常成功，但这种模型在小尺度上的预测仍然受到很差的检验。我研究的目标是利用我们的银河系邻居，如矮星系，围绕着银河系和恒星流旋转（由银河系潮汐干扰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信息。特别是，我计划使用盖亚卫星和其他大型天空调查（如LSST）的数据来寻找和描述恒星流。对恒星流的搜索和分析将帮助我了解银河系形成的过去历史。恒星流位置和速度的模型将告诉我银河系内部的质量分布，特别是暗物质的分布;对恒星流内部恒星密度分布的分析将使我能够探测到由小型暗物质晕产生的小型引力扰动。我还计划开发新的方法来搜索盖亚数据中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的星系，并且距离太阳更近，从而能够在小尺度上研究暗物质并搜索暗物质湮灭信号。最后，我还计划解决一个问题，这是非常重要的矮星系和恒星流的搜索在大型成像调查的天空：恒星星系分离。随着许多深度成像调查的进行和LSST调查即将到来，我们从微弱星系中分离微弱恒星的能力正在成为银河系周围微弱结构研究的主要限制因素。

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.