Cosmological elves: small scale tests of the cold dark matter paradigm

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The completion of photometric and redshift surveys of large portions of the sky have revolutionized our understanding of faint galaxies, extending the category of dwarf galaxies to luminosities so faint that they blur the traditional distinction between galaxies and star clusters. At the same time, advances in computational cosmology have led to improved predictions of the properties of the smallest dark matter halos able to harbour luminous galaxies in the current paradigm of structure formation, the LCDM model. The confrontation of data with model predictions on these small objects holds the promise to validate or challenge the established paradigm on scales beyond those used to constrain its main parameters. The time is ripe for a concerted effort designed to assess the cosmological significance of Nature's smallest extragalactic objects. I propose to study this topic using a variety of observational and theoretical tools, from detailed N-body simulation of the formation of dark matter halos, to gasdynamical simulation of the formation of luminous dwarf galaxies, to direct observational efforts designed to survey the faintest galaxies in our Local Universe and to understand their impact on the formation of our Milky Way galaxy.