Abstract

A fundamental difficulty in understanding galaxy formation is that it is a stochastic process by virtue of the Gaussian random initial conditions seeded in the early universe. One way to confront this limitation is to simulate sufficient numbers of galaxies in a large volume. However, this is computationally expensive and limits the resolution for a single galaxy. Alternatively, galaxy formation can be studied in the context of constrained realizations, where the initial conditions are modified in a well-defined way to control the properties of selected regions.

Building on the Hoffman-Ribak algorithm, we start from a reference simulation with fully random initial conditions, then make controlled changes to specific properties of a single halo (such as its mass and merger history). Our method demonstrably makes minimal changes to other properties of the halo and its environment, allowing us to isolate the impact of a given modification.

I will discuss several results of using these “genetically modified” initial conditions in both dark-matter-only as well as fully hydrodynamic cosmological simulations.