RAMSES-RT: Radiation hydrodynamics in the cosmological context

TL;DR

The paper introduces RAMSES-RT, a radiation hydrodynamics implementation in an AMR code that efficiently models radiative transfer in cosmological simulations, enabling detailed studies of galaxy formation.

Contribution

It presents a new moment-based RHD method integrated into RAMSES, capable of handling multiple sources efficiently and validated through comprehensive tests.

Findings

Efficient multi-group radiative transfer implementation.

Validation against other RHD codes shows high accuracy.

Suitable for cosmological and galaxy formation simulations.

Abstract

We present a new implementation of radiation hydrodynamics (RHD) in the adaptive mesh refinement (AMR) code RAMSES. The multi-group radiative transfer (RT) is performed on the AMR grid with a first-order Godunov method using the M1 closure for the Eddington tensor, and is coupled to the hydrodynamics via non-equilibrium thermochemistry of hydrogen and helium. This moment-based approach has the large advantage that the computational cost is independent of the number of radiative sources - it can even deal with continuous regions of emission such as bound-free emission from gas. As it is built directly into RAMSES, the RT takes natural advantage of the refinement and parallelization strategies already in place. Since we use an explicit advection solver for the radiative transport, the time step is restricted by the speed of light - a severe limitation that can be alleviated using the so--called "reduced speed of light" approximation. We propose a rigorous framework to assess the validity of this approximation in various conditions encountered in cosmology and galaxy formation. We finally perform with our newly developed code a complete suite of RHD tests, comparing our results to other RHD codes. The tests demonstrate that our code performs very well and is ideally suited for exploring the effect of radiation on current scenarios of structure and galaxy formation.