RAY-RAMSES: a code for ray tracing on the fly in N-body simulations

TL;DR

The paper introduces RAY-RAMSES, a novel on-the-fly ray tracing code integrated with N-body simulations that efficiently computes cosmological observables like weak lensing without extensive post-processing.

Contribution

It presents a new on-the-fly ray tracing method integrated into the RAMSES N-body code, enabling real-time computation of cosmological observables during simulations.

Findings

Good agreement with semi-analytical methods for lensing convergence maps

Efficient computation without large data storage requirements

Applicable to various cosmological effects like Sunyaev-Zel'dovich and Sachs-Wolfe

Abstract

We present a ray tracing code to compute integrated cosmological observables on the fly in AMR N-body simulations. Unlike conventional ray tracing techniques, our code takes full advantage of the time and spatial resolution attained by the N-body simulation by computing the integrals along the line of sight on a cell-by-cell basis through the AMR simulation grid. Moroever, since it runs on the fly in the N-body run, our code can produce maps of the desired observables without storing large (or any) amounts of data for post-processing. We implemented our routines in the RAMSES N-body code and tested the implementation using an example of weak lensing simulation. We analyse basic statistics of lensing convergence maps and find good agreement with semi-analytical methods. The ray tracing methodology presented here can be used in several cosmological analysis such as Sunyaev-Zel'dovich and integrated Sachs-Wolfe effect studies as well as modified gravity. Our code can also be used in cross-checks of the more conventional methods, which can be important in tests of theory systematics in preparation for upcoming large scale structure surveys.