GenetIC -- a new initial conditions generator to support genetically modified zoom simulations

TL;DR

genetIC is a novel code for creating precise, customizable initial conditions in cosmological simulations, enabling targeted modifications of specific regions while maintaining statistical consistency, supporting nested zoom regions and constrained conditions.

Contribution

it introduces a Fourier-space filtering method for efficient, accurate genetic modifications in zoom initial conditions, enhancing flexibility and precision in cosmological simulations.

Findings

achieves sub-percent accuracy in modifications

supports nested zoom regions with consistent resolution

enables constrained initial conditions matching local universe structures

Abstract

We present genetIC, a new code for generating initial conditions for cosmological N-body simulations. The code allows precise, user-specified alterations to be made to arbitrary regions of the simulation (while maintaining consistency with the statistical ensemble). These "genetic modifications" allow, for example, the history, mass, or environment of a target halo to be altered in order to study the effect on their evolution. The code natively supports initial conditions with nested zoom regions at progressively increasing resolution. Modifications in the high-resolution region must propagate self-consistently onto the lower resolution grids; to enable this while maintaining a small memory footprint, we introduce a Fourier-space filtering approach to generating fields at variable resolution. Due to a close correspondence with modifications, constrained initial conditions can also be produced by genetIC (for example with the aim of matching structures in the local Universe). We test the accuracy of modifications performed within zoom initial conditions. The code achieves sub-percent precision, which is easily sufficient for current applications in galaxy formation.