RAyMOND: An N-body and hydrodynamics code for MOND

TL;DR

RAyMOND is a modified version of the RAMSES code that implements two formulations of MOND gravity, enabling detailed simulations of galaxy dynamics under alternative gravity theories.

Contribution

The paper introduces a new implementation of MOND in the RAMSES code, including both AQUAL and QUMOND formulations, for improved galaxy interaction simulations.

Findings

Code successfully implements MOND in RAMSES

Effective in serial and parallel idealised tests

Enables study of galaxy interactions under modified gravity

Abstract

The LCDM 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 cold dark matter 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 deserves 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 (AQUAL) formulation as well as the simpler quasi-linear formulation (QUMOND). The relevant modifications necessary for the Poisson solver in RAMSES are discussed in detail. Using idealised tests, in both serial and parallel runs, we demonstrate the effectiveness of the code.