RAyMOND: an N-body and hydrodynamics code for MOND

The Λ cold dark matter (ΛCDM) concordance cosmological model is supported by a wealth of observational evidence, particularly on large scales. At galactic scales, however, the model is poorly constrained and recent observations suggest a more complex behaviour in the dark sector than may be accommodated by a single CDM component. Furthermore, a modification of the gravitational force in the very weak field regime may account for at least some of the phenomenology of dark matter. A well-known example of such an approach is MOdified Newtonian Dynamics (MOND). While this idea has proven remarkably successful in the context of stellar dynamics in individual galaxies, the effects of such a modification of gravity on galaxy interactions and environmental processes deserve further study. To explore this arena, we modify the parallel adaptive mesh refinement code ramses to use two formulations of MOND. We implement both the fully non-linear aquadratic Lagrangian formulation and the simpler quasi-linear formulation. The relevant modifications necessary for the Poisson solver in ramses are discussed in detail. Using idealized tests, in both serial and parallel runs, we demonstrate the effectiveness of the code.