Galaxy formation plays a central role in modern cosmology as many cosmological probes involve galaxies, from mapping their spatial distribution to counting galaxy clusters, to studying the distorting effect of gravitational lensing on the galaxies by the intervening
dark matter. On large scales, we expect galaxies to trace the underlying dark matter distribution. We can also use lensing to infer the "clumpy-ness" of dark matter around and in-between galaxies. Measuring the galaxy and cluster distribution across cosmic time also helps us measure the growth of large-scale structure in the Universe, as the dark matter collapses under its own gravity, building up larger and larger structures such as clusters.
The Universe also contains “normal” matter, or baryons, which is a complex mixture of galaxies and intergalactic gas. Galaxies form from this gas (which is mainly hydrogen and helium), but also return material in the form of energetic winds and jets, powered by exploding stars and super-massive black holes. Understanding the role of this “feedback” is crucial to our understanding of galaxy formation as a whole, and cosmology is now reaching a level of precision where we must take these baryonic effects into account.
At JBCA, we use detailed computer simulations to study how galaxies and clusters form with our main aim being to improve our understanding of baryonic physics in cosmology. Our simulations start with realistic cosmological initial conditions, contain both the dark matter and baryonic components, and include the effects of dark energy on the expansion of the universe.
We include both gravity and hydrodynamics in our calculations, as well as model the key astrophysical processes associated with galaxy formation: gas cooling and heating; star formation; growth of super-massive black holes and feedback from massive stars and active galactic nuclei. We compare our simulations to a range of observational data, from radio through optical/infrared to X-ray wavelengths, and are involved in a number of observational programmes. Our work is particularly focused on galaxy clusters, the most extreme environments for galaxy formation and also where the most massive galaxies can be found.