Enzo+Moray: Radiation Hydrodynamics Adaptive Mesh Refinement Simulations
  with Adaptive Ray Tracing
  We describe a photon-conserving radiative transfer algorithm, using a
spatially-adaptive ray tracing scheme, and its parallel implementation into the
adaptive mesh refinement (AMR) cosmological hydrodynamics code, Enzo. By
coupling the solver with the energy equation and non-equilibrium chemistry
network, our radiation hydrodynamics framework can be utilised to study a broad
range of astrophysical problems, such as stellar and black hole (BH) feedback.
Inaccuracies can arise from large timesteps and poor sampling, therefore we
devised an adaptive time-stepping scheme and a fast approximation of the
optically-thin radiation field with multiple sources. We test the method with
several radiative transfer and radiation hydrodynamics tests that are given in
Iliev et al. (2006, 2009). We further test our method with more dynamical
situations, for example, the propagation of an ionisation front through a
Rayleigh-Taylor instability, time-varying luminosities, and collimated
radiation. The test suite also includes an expanding H II region in a
magnetised medium, utilising the newly implemented magnetohydrodynamics module
in Enzo. This method linearly scales with the number of point sources and
number of grid cells. Our implementation is scalable to 512 processors on
distributed memory machines and can include radiation pressure and secondary
ionisations from X-ray radiation. It is included in the newest public release
of Enzo.
