The Relationship between gas and galaxies.

The process by which matter collapsed gravitationally to form the large scale structure of the Universe is well understood, despite the fact that we still do not know what makes up the 'dark matter' which dominates this collapse. What is not yet understood is how baronic matter then falls into these gravitational potential wells to form stars and galaxies. Simple models suggested that essentially all of the gas in the Universe should have been converted into stars by the present day, while observations show that in fact only a tiny fraction of the gas has been converted. The answer to this conundrum has to include a large amount of 'feedback' where the formation of a first generation of stars generates shocks and winds that prevents the subsequent collapse of further gas into that gravitational potential well. Detailed numerical models including plausible feedback mechanisms have now been created, but have not been tested by being compared with the real universe. To do this we will measure the properties of the gas using HST, and also large ground based telescopes (where we can measure the distances to large samples of faint galaxies and the high redshift gas properties can be seen).