Does Modified Gravity Predict Fast Stellar Bars in Spiral Galaxies?

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, that is, nonlocal gravity and scalar–tensor–vector gravity, known as MOG, and ignore the existence of a dark matter (DM) halo. We construct the same models as in the standard DM 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 DM case, but the 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 is to show that the above-mentioned differences, with an emphasis on the speed of the bars, are independent of the initial density profile of the adopted disk and 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 bars. Our results imply that, contrary to the DM models, bars in modified gravity are fast rotators that never leave the fast-bar region until the end of the simulation.