Stellar Bar Evolution in the Absence of Dark Matter Halo

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 galaxy models with a dark matter halo. On the other hand, the initial random velocities and Toomre’s local stability parameter are the same for all of 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 are smaller in MOG. On the other hand, the maximum value of the bar in MOG is smaller than that in the Newtonian models. It is shown that although the live dark matter halo may support bar instability, MOG has stabilizing effects. Furthermore, we show that MOG supports fast pattern speeds, and unlike in the dark matter halo models, the pattern speed does not decrease with time. These differences, combined with the relevant observations, may help to distinguish between dark matter and modified gravity in galactic scales.