The Role of Gas in Galaxy Evolution

How do galaxies get their gas and how do they lose it? Theories of galaxy formation predict that the growth of galaxies is regulated by the infall of hydrogen gas. This gas is the fuel for star formation. When galaxies run out of gas star formation stops. Interestingly, observationally we know much more about the stars in galaxies and how the star formation rate has evolved over time than we know about the gas. The gas is hard to observe. Currently a renaissance is taking place in observational radio astronomy, new telescopes have been developed, which can image this gas, and even better ones are being constructed. I will show what we already have learned, discuss remaining puzzles and outline what the future might bring.