Stellar Bar evolution in the absence of dark matter halo

TL;DR

This study compares stellar bar evolution in galaxy models with and without dark matter halos, using MOG as an alternative gravity theory, revealing significant differences in bar growth and dynamics.

Contribution

It demonstrates how modified gravity (MOG) influences bar formation and evolution differently from dark matter halos in high-resolution galaxy simulations.

Findings

Bar growth rate is smaller in MOG

Maximum bar strength is reduced in MOG

MOG supports faster pattern speeds without slowdown

Abstract

We study the stellar bar growth in high resolution numerical galaxy models with and without dark matter halos. In all models the galactic disk is exponential and the halos are rigid or live Plummer spheres. More specifically, when there is no dark matter halo, we modify the gravitational force between point particles. To do so we use the weak field limit of an alternative theory of dark matter known as MOG in the literature. The galaxy model in MOG has the same initial conditions as in galaxy models with dark matter halo. On the other hand, the initial random velocities and the Toomre's local stability parameter are the same for all the models. We show that the evolution and growth of the bar in MOG is substantially different from the standard cases including dark matter halo. More importantly, we find that the bar growth rate and its final magnitude is smaller in MOG. On the other hand, the maximum value of the bar in MOG is smaller than the Newtonian models. It is shown that although the live dark matter halo may support the bar instability, MOG has stabilizing effects. Furthermore, we show that MOG supports fast pattern speeds, and unlike in the dark matter halo models pattern speed does not decrease with time. Theses differences, combined with the relevant observations, may help to distinguish between dark matter an modified gravity in galactic scales.