Title: Small-scale structure in cold dark matter: from ultra-faint dwarfs to prompt cusps
Abstract: In our present paradigm of galaxy formation, the onset of structure is brought about via the gravitational collapse of (cold) dark matter, which subsequently acts as the scaffolding for the visible universe. A vigorous programme of numerical simulations has established several features of the dark matter model: the formation of haloes, and how their structure and abundance is influenced by the particle physics of the underlying model. The smallest visible galaxies—so-called “ultra-faint dwarfs”—are fossil records of an early phase of galaxy formation in the Universe and their assembly provides strong clues into the Epoch of Reionisation, galactic feedback, and the nature of the dark matter particle. Yet, the cold dark matter model predicts the formation of structure many orders-of-magnitude below the scale where galaxy formation ends, where individual dark matter haloes have masses comparable to that of the Earth. In this talk, I will discuss some of the progress we have made in understanding this regime using numerical simulations, and what their implications are for understanding the physics of galaxy formation, the nature of dark matter, and our prospects for detecting dark matter in the future.