Smoothed Particle Radiation Hydrodynamics: Two-Moment method with Local
  Eddington Tensor Closure
  We present a new radiative transfer method (SPH-M1RT) that is coupled
dynamically with smoothed particle hydrodynamics (SPH). We implement it in the
(task-based parallel) SWIFT galaxy simulation code but it can be
straightforwardly implemented in other SPH codes. Our moment-based method
simultaneously solves the radiation energy and flux equations in SPH, making it
adaptive in space and time. We modify the M1 closure relation to stabilize
radiation fronts in the optically thin limit. We also introduce anisotropic
artificial viscosity and high-order artificial diffusion schemes, which allow
the code to handle radiation transport accurately in both the optically thin
and optically thick regimes. Non-equilibrium thermo-chemistry is solved using a
semi-implicit sub-cycling technique. The computational cost of our method is
independent of the number of sources and can be lowered further by using the
reduced speed of light approximation. We demonstrate the robustness of our
method by applying it to a set of standard tests from the cosmological
radiative transfer comparison project of Iliev et al. The SPH-M1RT scheme is
well-suited for modelling situations in which numerous sources emit ionising
radiation, such as cosmological simulations of galaxy formation or simulations
of the interstellar medium.
