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Constrained Simulations of the Local Universe

The main goal of the study of galaxies and large scale structure formation is to achieve a physical understanding of how the observed structures formed out of cosmological initial conditions.

Numerical simulations have been the driving force behind much of the theoretical progress in this field. However, numerical simulations have their draw backs: any given simulation struggles between having the desired spatial resolution and representing the desired representative volume.

A new complementary approach to cosmological simulations has been introduced over the last few years by the PIs of the CLUES-project. The idea is to use observations of the mass distribution in the nearby universe as constraints imposed on the initial conditions of the simulations, resulting in so-called “constrained simulations”. Such constrained simulations by design reproduce the local large scale structure and the cosmic web. We use the term ‘local’ to mean the neighborhood within a few tens of megaparsecs around the Milky Way. This method introduces a paradigm shift in the field of numerical simulations: no longer are computational cosmologists forced to simulate random volumes in aribitrary environments. With this new approach, simulations are designed and tailor-made to reproduce the unique local universe and not a representative part of the entire universe. They thus provide the ideal numerical laboratory to study the formation of the Milky Way and the Local Group.

The algorithm of constrained realizations of Gaussian fields provides a very attractive way of imposing observational data as constraints on the initial conditions. As observational constraints we use the radial velocities of galaxies drawn from the MARK III, SBF and the local volume galaxy catalog as well as the position of nearby X-ray selected clusters of galaxies.