Does modified gravity predict fast stellar bars in spiral galaxies?

Abstract

The evolution of disk galaxies in modified gravity is studied by using high-resolution N-body simulations. More specifically, we use the weak field limit of two modified gravity theories, i.e., nonlocal gravity (NLG) and scalar-tensor-vector gravity known as MOG, and ignore the existence of dark matter halo. On the other hand, we construct the same models in the standard dark matter model and compare their dynamics with the galactic models in modified gravity. It turns out that there are serious differences between galactic models in these different viewpoints. For example, we explicitly show that the galactic models in modified gravity, host faster bars compared to the dark matter case. On the other hand, final stellar bars are weaker in modified gravity. These facts are not new and have already been reported in our previous simulations for exponential galactic models. Therefore, our main purpose in this study is to show that the above-mentioned differences, with emphasis on the speed of the bars, are independent of the initial density profile of the adopted disk/halo. To do so, we employ different profiles for the disk and halo and show that the results remain qualitatively independent of the initial galactic models. Moreover, a more accurate method has been used to quantify the kinematic properties of the stellar bar. Our results imply that contrary to the dark matter models, bars in modified gravity are fast rotators which never leave the fast-bar region until the end of the simulation.