Near-field cosmology - tagging the lowest-mass galaxies

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.