sCOLA: The N-body COLA Method Extended to the Spatial Domain

TL;DR

sCOLA extends the N-body COLA method to the spatial domain, enabling efficient, localized large-scale structure simulations by decoupling far and near gravitational fields, thus improving computational speed and scalability.

Contribution

The paper introduces sCOLA, a novel extension of the COLA method that localizes gravity in N-body simulations, facilitating zoom-in simulations and parallel computation for large-scale structure modeling.

Findings

sCOLA accurately reproduces standard N-body results in small volumes.

It enables efficient zoom-in and large ensemble simulations.

sCOLA is compatible with the original temporal COLA method.

Abstract

We present sCOLA -- an extension of the N-body COmoving Lagrangian Acceleration (COLA) method to the spatial domain. Similar to the original temporal-domain COLA, sCOLA is an N-body method for solving for large-scale structure in a frame that is comoving with observers following trajectories calculated in Lagrangian Perturbation Theory. Incorporating the sCOLA method in an N-body code allows one to gain computational speed by capturing the gravitational potential from the far field using perturbative techniques, while letting the N-body code solve only for the near field. The far and near fields are completely decoupled, effectively localizing gravity for the N-body side of the code. Thus, running an N-body code for a small simulation volume using sCOLA can reproduce the results of a standard N-body run for the same small volume embedded inside a much larger simulation. We demonstrate that sCOLA can be safely combined with the original temporal-domain COLA. sCOLA can be used as a method for performing zoom-in simulations. It also allows N-body codes to be made embarrassingly parallel, thus allowing for efficiently tiling a volume of interest using grid computing. Moreover, sCOLA can be useful for cheaply generating large ensembles of accurate mock halo catalogs required to study galaxy clustering. Surveys that will benefit the most are ones with large aspect ratios, such as pencil-beam surveys, where sCOLA can easily capture the effects of large-scale transverse modes without the need to substantially increase the simulated volume. As an illustration of the method, we present proof-of-concept zoom-in simulations using a freely available sCOLA-based N-body code.