Groups: Millennium simulations

The Millennium Simulation is a 10¹⁰ particle cosmological simulation carried out at the Max Planck Institute for Astrophysics in Garching, Germany which tracks the evolution of structure in the Universe from shortly after the Big Bang to the present day. This original simulation include only dark matter, which dominates the mass of the Universe, and interacts only through gravity.

The full Millennium Simulation, showing the filamentary structure of the dark matter at the end of the simulation, which corresponds to the present epoch.

Close-up of a galaxy cluster within the simulation. Clusters lie at the intersection of the large scale filaments, and grow as galaxies and groups fall into them. The small yellow blobs in the picture correspond to the dark halos of individual galaxies

The behaviour of normal atomic matter is much more complicated, and follow-up simulations using a supercomputer in Nottingham, also include normal (baryonic) matter, and attempt to model the extra astrophysics (heating, cooling, shocks, star formation, supernovae etc.) which they bring with them. The Birmingham group is involved in this collaboration, the aim being to compare the results of different simulations with our observations of galaxy groups and clusters, so as to test and improve the physics in the models. We are also looking for fossil groups in the simulated data, in order to understand how these remarkable systems form.

These images show hot gas within the cluster whose dark matter distribution was shown previously. In the image to the left, no cooling processes are included in the simulation, and the gas is heated only through compression and shocks. It is found that galaxy groups in this simulation contain too much gas to match observations. In the simulation shown on the right, the gas is heated at a high redshift, which leads to a much smoother gas distribution at zero redshift, and a better match to our observations.

Researchers: Alastair Sanderson, Ali Dariush, Trevor Ponman, Somak Raychaudhury