The velocity field in MOND cosmology

TL;DR

This study uses the RAyMOND simulation code to explore how Modified Newtonian Dynamics (MOND) affects cosmic structure formation, especially the velocity field, suggesting a distinctive observational signature in intermediate density regions.

Contribution

It demonstrates the application of RAyMOND for cosmological simulations of MOND and analyzes the impact on the velocity field compared to $ ext{Lambda}$CDM models.

Findings

MOND leads to a significant enhancement of the velocity field.

The velocity signature may be most observable in cluster outskirts and filaments.

Simulation results differ from standard $ ext{Lambda}$CDM predictions.

Abstract

The recently developed code for N-body/hydrodynamics simulations in Modified Newtonian Dynamics (MOND), known as RAyMOND, is used to investigate the consequences of MOND on structure formation in a cosmological context, with a particular focus on the velocity field. This preliminary study investigates the results obtained with the two formulations of MOND implemented in RAyMOND, as well as considering the effects of changing the choice of MOND interpolation function, and the cosmological evolution of the MOND acceleration scale. The simulations are contrived such that structure forms in a background cosmology that is similar to $\Lambda$CDM, but with a significantly lower matter content. Given this, and the fact that a fully consistent MOND cosmology is still lacking, we compare our results with a standard $\Lambda$CDM simulation, rather than observations. As well as demonstrating the effectiveness of using RAyMOND for cosmological simulations, it is shown that a significant enhancement of the velocity field is likely an unavoidable consequence of the gravitational modification implemented in MOND, and may represent a clear observational signature of such a modification. It is further suggested that such a signal may be clearest in intermediate density regions such as cluster outskirts and filaments.