GALGASSKA · How do galaxies get their gas?

Observing the evolution of galaxies over cosmic time is one of the key priorities for the new Square Kilometre Array (SKA), the next-generation radio telescope that will be built in South Africa and Australia over the next decade. Its large size and extreme sensitivity mean it will have a huge impact on astrophysics. In the run-up to the SKA, several SKA-precursor telescopes are starting to probe SKA science already. We describe a project covering an important aspect of one of the SKA science questions, namely to establish where the gas in galaxies comes from. Galaxies seem to form stars at a rate that makes it impossible to sustain their current gas reservoirs over the lifetime of the universe. They must therefore continuously acquire pristine gas from somewhere. Theory predicts the existence of a ""cosmic web"" of gas and dark matter surrounding the galaxies which provides this new fuel. With ultra-sensitive observations it will be possible to directly observe this ""accretion"" of gas. Using the Dutch APERTIF, the Australian ASKAP and the South African MeerKAT SKA precursor telescopes (this project has already been allocated 8 months of observing time on the latter), we will directly observe the presence and establish the importance of accretion. The outcome will have a significant impact on our current models for galaxy evolution, and will guide future SKA work. This project also fulfills the recent call of the European Parliament for greater collaboration with Africa in the field of radio astronomy (Written Declaration 45/2011).""