Quenching star formation via hierarchical clustering of galaxies

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The bewildering variety of structure in the Universe around us today is one of the biggest mysteries in astronomy. How did a Universe that started off so simply, as smoothly distributed hydrogen gas, produce galaxies with such a wide range of shapes, sizes and ages, arranged in a complex, web-like structure? More specifically puzzling is the fact that some unknown agent has been acting to prevent stars and galaxies from forming. This mechanism must not be equally efficient everywhere, or at all times, in order to give rise to the variety of galaxies we see today. As time goes on, galaxies gather together into groups, and evidence is mounting that it is within this group environment that galaxies undergo the profound change that renders them unable to form new stars. My research is aimed at improving our understanding of these poorly studied systems, to help identify and quantify the interesting astrophysics that we know must be present. Through careful observations and theoretical modeling I expect to be able to characterise the timescale over which star formation activity is shut off in groups, and how this might depend on the group mass or surrounding environment. As galaxy groups are the most common environment today, and as their abundance changes greatly with time, the results of this research will have profound consequences for our understanding of galaxy formation and evolution in general.