A scheme for radiation pressure and photon diffusion with the M1 closure in RAMSES-RT

TL;DR

This paper presents an enhanced version of RAMSES-RT that incorporates radiation pressure, improved diffusion treatment, and relativistic effects, validated through comprehensive tests for realistic astrophysical scenarios.

Contribution

The paper introduces new features in RAMSES-RT, including radiation pressure, accurate diffusion in optically thick media, and relativistic corrections, enabling more realistic radiation feedback simulations.

Findings

Validated the M1 closure for Eddington tensor in astrophysical settings

Demonstrated convergence of radiation diffusion scheme in optically thick media

Simulated radiation-gravity competition and Rayleigh-Taylor instabilities

Abstract

We describe and test an updated version of radiation-hydrodynamics (RHD) in the RAMSES code, that includes three new features: i) radiation pressure on gas, ii) accurate treatment of radiation diffusion in an unresolved optically thick medium, and iii) relativistic corrections that account for Doppler effects and work done by the radiation to first order in v/c. We validate the implementation in a series of tests, which include a morphological assessment of the M1 closure for the Eddington tensor in an astronomically relevant setting, dust absorption in a optically semi-thick medium, direct pressure on gas from ionising radiation, convergence of our radiation diffusion scheme towards resolved optical depths, correct diffusion of a radiation flash and a constant luminosity radiation, and finally, an experiment from Davis et al. of the competition between gravity and radiation pressure in a dusty atmosphere, and the formation of radiative Rayleigh-Taylor instabilities. With the new features, RAMSES-RT can be used for state-of-the-art simulations of radiation feedback from first principles, on galactic and cosmological scales, including not only direct radiation pressure from ionising photons, but also indirect pressure via dust from multi-scattered IR photons reprocessed from higher-energy radiation, both in the optically thin and thick limits.