Near-field cosmology - tagging the lowest-mass galaxies

星系的形成和演化是当代天体物理学中最令人感兴趣的领域。在这种情况下，研究星系形成的一个关键方法被称为“近场宇宙学”，即研究银河系内外附近系统中已分解的恒星群。本地群中的这些小尺度结构可能为目前最成功的宇宙结构形成和演化的宇宙学模型提供一些最具挑战性的测试。这个提议的目的是研究最微弱的矮星系在更大星系的形成和演化中的作用。仅在过去的两年里，我们就发现了十几个这样不显眼的星系。因此，本课题旨在从恒星光谱学的角度研究它们的化学演化、恒星形成历史及其动力学特性。这些星系现在被认为是大型星系的基本组成部分，尽管这种观点仍然存在争议，因为它们的许多特性与银河系中的恒星不同。在这项工作中，我将把重点放在最近发现的星系上，这些星系是迄今为止已知的最微弱、质量最小、金属含量最低的星系，对它们的了解仍然很少。我将通过高分辨率光谱进行化学元素丰度分析来实现这些目标，在那里我将测量相对于金属贫乏参考星的丰度。这将与宽视场光度法，特别是中分辨率光谱学相辅相成。这种组合将使我能够有效地确定这些星系的空间分辨恒星形成和它们的富集历史，然后可以将其与银河系的组成部分进行比较，以了解这些小系统对大星系形成的贡献程度。矮星系，特别是矮球星系，很可能是高度暗物质主导的系统。通过研究它们的运动特性，我从中分辨率光谱的径向速度测量和随后的动力学建模中确定了它们的运动特性，我可以确定星系的质量和密度分布，估计它们的暗物质含量，从而对宇宙中这种难以捉摸的成分的特性施加重要的限制。

The formation and evolution of galaxies is a field of paramount interest in contemporary astrophysics. In this context, one key approach to the study of galaxy formation is dubbed 'near-field cosmology', that is the study of resolved stellar populations in nearby systems in and around the Milky Way. These small scale structures in the Local Group may provide some of the most challenging tests of the currently most successful cosmological models for structure formation and evolution in the Universe. This proposal aims at investigating the role of the faintest dwarf galaxies in the formation and evolution of larger galaxies. The last two years alone have seen the discovery of a dozen of these inconspicuous systems. Thus this proposal aims to study their chemical evolution, star formation histories and their dynamical properties from stellar spectroscopy. These galaxies are nowadays believed to be the fundamental building blocks of large galaxies, although this view is still controversial, as many of their properties are at variance with the stars in the Milky Way. In this work I will focus on the most recently discovered galaxies, which are the faintest, least massive and most metal poor galaxies known to date and still poorly understood. I will achieve these aims by performing chemical element abundance analyses from high-resolution spectroscopy, where I will measure abundances relative to metal poor reference stars. This will be complemented with wide-field photometry and especially medium-resolution spectroscopy. This combination will enable me to efficiently determine these galaxies' spatially resolved star formation and their enrichment histories, which then can be compared to the components of the Galaxy to understand the extent to which these small systems contributed to the build-up of the larger galaxies. The dwarf galaxies, in particular the dwarf spheroidals, are likely highly dark matter dominated systems. By investigating their kinematic properties, which I determine from radial velocity measurements from medium-resolution spectra and subsequent dynamical modeling, I can determine the galaxies' mass and density profiles, estimate their dark matter content and thus place important constraints on the properties of this evasive constituent of the Universe.