The relationship between the formation of galaxies and large-scale structures

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When we look up at the night sky, we see that galaxies seem to be arranged in a particular way. One might expect that galaxies would be distributed randomly, much as grains of sand would if you threw a handful across the floor, but instead, they seem to trace elegant structures; galaxy clusters are connected to each other by long filaments, interspersed with large voids, where few or no galaxies are seen. The reason why galaxies are arranged this way is deeply mysterious; we know that, when the Universe was very young, it was a very smooth, even place, so how did the Universe go from being homogeneous and smooth just after the Big Bang to the clumpy, clustered, irregularly structured Universe we see today? A second problem, concerns how bright and active we see galaxies to be. Nearby galaxies are quiet, placid things where not an awful lot happens; at most a few stars are born and a few die each year. For galaxies a long long way away, things are completely different; they are much more violent - forming hundreds, if not thousands of new stars each year - and are many hundreds of times brighter than local galaxies. Furthermore, these distant galaxies seem to be colliding with each other much more frequently than galaxies nearby us, and it is suspected that these galaxy collisions are in some way responsible for their huge star formation rates. The central puzzle remains though; why is the Universe nearby to us such a quiet, unassuming place, while the distant Universe is so violent and active? In recent years, astronomers have started to suspect that the answer to both these questions may lie in the same place, namely the mysterious and poorly understood `dark' matter. Dark matter is so called because it has the singularly disobliging tendency not to emit any light at all, at any wavelength, which makes it impossible to see with conventional telescopes. If however we look at the way stars move in galaxies, we can see that there must be an awful lot of dark matter in these galaxies (something like ten times the mass of visible matter), as we can see the dark matter pulling the stars around. We might suspect that this dark matter may have something to do with how galaxies are distributed on the sky, simply because there's so much of it. We might also expect that galaxies should trace the dark matter, with more galaxies occurring in regions of more dark matter and vice versa, because dark matter is comprised, in part, of the gas and dust from which stars are formed. So, if we want to work out why galaxies trace the structures they do, or how galaxies are formed, we must work out how galaxies trace the underlying dark matter, and how this dark matter affects galaxy formation. This is one of the most important problems in astronomy today, as it literally underpins everything we see. A series of new telescopes hold the promise of a revolution in our understanding of how galaxies, and clusters and filaments, form. The goal of the fellowship will be to combine data from these new facilities with the latest computer models and simulations, to make great strides in our understanding of galaxy and structure formation. Work using optical data will focus on how the stars in very distant galaxies are assembled. Does it happen gradually or all at once? When during the history of the Universe do most stars in galaxies form? What parts of the Universe will eventually become the densest galaxy clusters we see nearby us, and which will become large, empty voids? Work in the infrared on the other hand will focus on galaxies with huge bursts of star formation - these are thought to be the formation events of some of the biggest galaxies in the Universe. By studying how these distant infrared bright galaxies are grouped on the sky, and exactly how the star formation within them is occurring, I will relate how and when they form to the dark matter that surrounds them.