The Stromlo Missing Satellites Survey

According to cosmological theory, density fluctuations of Cold Dark Matter (CDM) form the first structures in the Universe. The gravitational potential wells of these dark matter halos suck in primordial gas and provide the seeds for the formation of stars via energy dissipation and cooling, a billion years after the Big Bang. The observational Universe today is filled with these galaxies, the prime repositories of shining baryonic matter. For obvious reasons, most of the detected and catalogued galaxies are intrinsically the largest and the brightest, those that can be seen from the greatest distance and are most easily studied against the night sky. Ironically, a major limitation on our ability to develop a consistent model that describes how galaxies emerged out of dark matter comes from the incompleteness of our picture of the nearby universe, in particular from the lack of a detailed understanding of the phenomenon dwarf galaxies. Dwarf galaxies are stellar systems composed almost entirely of dark matter with a minimum mass of the order of 10 solar masses. Examples have been discovered orbiting the Milky Way and Andromeda galaxies. Extreme low star densities make them transparent and hard to find, but they seem to dominate by numbers any volume in space and were more numerous in the cosmological past. CDM theory tells us that the dark matter mini halos and their optical manifestations, the dwarf galaxies, are the building blocks of larger galaxies like our Milky Way. Hence, if we want to shed light on the nature of dark matter and understand the driving mechanisms of galaxy formation/evolution we have to spend a disproportionate amount of effort on finding and physically characterising the faintest, most elusive galaxies that exist in the Universe.