Bar formation and galaxy interactions in MOND

TL;DR

This paper introduces a new N-body simulation code for galactic dynamics in MOND, revealing differences in bar formation and galaxy interactions compared to dark matter models, with implications for understanding galactic evolution.

Contribution

The paper presents the first self-consistent N-body code for MOND, including adaptive mesh refinement, to compare galaxy evolution and interactions with dark matter models.

Findings

Galaxies in MOND form stronger, faster bars.

Merging times are longer in MOND due to reduced dynamical friction.

Different interaction morphologies are observed between models.

Abstract

The LCDM model is the most commonly admitted to describe our Universe. In spite of a great success with regard to the large scale structure formation, some problems are still unresolved at galactic scales. Alternative scenarios have to be explored such as modified gravity. We have developed an N-body code able to solve in a self consistent way the galactic dynamics in MOND. The first version of the code consists in solving the modified Poisson equation on a uniform Cartesian grid to derive the gravitational force on each particle. With it, we study the evolution of isolated galaxies, like the bar instability, the angular momentum transfer, etc. Galaxies in MOND are found to form stronger bars, faster than in Newtonian dynamics with dark matter. In a second step, we implement an adaptive mesh refinement technique in the code, allowing to run more contrasted simulations on larger scales, like interacting galaxies. During an interaction, the dynamical friction forces are less important in MOND, and merging times are longer than in DM models. The different morphologies of interacting galaxies in the two models are discussed. All simulations are performed in both frameworks of modified gravity and Newtonian gravity with dark matter with equivalent initial conditions.