C1 Simulating the Galaxy Population of Dark Energy Universes
The reconstruction of the expansion history of the Universe has become a primary goal of observational cosmology. One of the most promising emerging techniques relies on observations of the baryonic acoustic oscillations (BAOs) in the matter distribution at low and intermediate redshifts. Ongoing galaxy redshift surveys such as Sloan/BOSS
aim to hugely expand the surveyed volume and the available galaxy numbers. However, the ability of the surveys to constrain dark energy depends on an accurate understanding of systematic effects, like the scale-dependent bias between the observed luminous red galaxies and the underlying matter distribution or the impact of mildly non-linear evolution on the BAO features themselves.
Simulations of the galaxy formation process are arguably the most powerful technique to accurately quantify these effects and will be needed to fully exploit the observational data. In this project, we carry out and analyze an extremely large N-body simulation, with of the order 200-300 billion particles in a cosmological volume about 3 Gpc across. To cope with the enormous data size, we construct detailed Dark Matter merger history trees on the fly during the simulation. Using recently developed novel techniques, these Dark Matter merger trees can be scaled accurately different cosmologies with appropriate adjustments of the involved time, mass, and length scales, and adjustment of the linear power.
Applying semi-analytic galaxy formation simulations to each of the rescaled trees, allows a prediction of the galaxy distribution for a broad class of cosmologies and galaxy formation models without the need to repeat the computationally expensive parent simulation. As a result, it becomes possible to include the parameters of galaxy formation models in maximum likelihood analyses of the observational data, leading to more general and more robust constraints on dark energy parameters which specifically account for statistical cross-talk between galaxy formation and cosmology.
Role within the Transregional Collaborative Research Centre
This project plays a crucial role for all the observationally oriented projects in this Transregio, as it can provide theoretical mock catalogues that closely mimic the observational data sets, ranging from clusters of galaxies at different redshifts, to samples of luminous red galaxies, or high-redshift quasars. The observational programs can use these mock catalogues both to test for systematic effects and to forecast their statistical errors.