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Research Interests

Your main research interests concern the computer modelling of galaxy formation.

How very unpleasant: here you are stuck in a meeting with a pack of observers and instrument builders! New telescopes and detectors are all very good: they have led to a revolution in observational astronomy. The observers think that they are smart, but it is only thanks to these new telescopes that all the exciting recent progress has been made in the study of the high redshift universe. Even more dramatic advances in computer power have had a similar effect on theoretical studies of the early universe. For the first time, it is now becoming possible to simulate a representative chunk of the universe in a computer.

You have long been pioneering this approach, using a combination of analytic maths, n-body simulations and hydrodynamics codes to simulate galaxy and cluster formation. You start your simulations with a uniform gas-filled section of the universe, rippled with tiny primordial fluctuations. You then let the code run: slowly, the overdense regions suck matter (both dark and baryonic) in towards them. At redshift tex2html_wrap_inline82 , many tiny ( tex2html_wrap_inline84 ) matter concentrations collapse: to stop these from forming vast numbers of stable globular clusters, you add a line to your computer code, which means that the first stars that form in these tiny concentrations go supernova and blow the remaining gas out of the gravitational potential well.

As time continues, the matter starts to form sheets and filaments: the exact shapes and densities determined by the cosmology and form of primordial fluctuations you chose in this simulation. By redshift ten, some knots (where filaments and sheets join) are getting dense enough to form galaxies, and the first light in the universe switches on. You had to cheat here a bit: you have no idea what densities are needed to trigger galaxy formation: you just chose a number that made your simulation come out right at redshift zero.

By redshift 5, clusters of galaxies are centred on these knots. These clusters have not yet assembled much matter, but maybe enough has assembled to power quasars.

By redshift 2, more galaxies have formed, filling in the sheets and filaments. Galaxy formation rates peak at redshift one, after which most of the gas has been consumed, and the universe quietens down, and the galaxies just drift around, slowly being sucked into the high dark matter concentrations in the sheets (`great walls') and knots (` superclusters').

The remarkable thing is that the predictions from these simulations quite accurately match the observations of Ly-break galaxies and QSO absorption-line systems. The galaxies seen at high redshifts are indeed small, strongly clustered, and forming stars slowly and gently, just as you predict. Just as you predict, the star formation rate in the universe seems to peak around redshift one.

next up previous
Next: Proposed Facility Up: You are from The Previous: You are from The

Paul Francis
Sun Aug 30 11:56:56 EST 1998