Description
Galactic bars rotate at different rates, both in the observed Universe and in simulations, but the precise reasons for these various pattern speeds are not fully understood. We use a high temporal resolution version of the Auriga suite of magneto-hydrodynamical cosmological zoom-in simulations to identify the galaxy properties and histories that set the pattern speeds of bars. In contrast with generally expected evolution, we find that the bars in these simulations do not typically slow down from formation to z = 0, instead preferentially speeding up. This implies that dynamical friction from the dark matter halo does not dominate the evolution of these bars. We find that the faster bars are those which are stronger, older, and hosted in more massive, baryon-dominated galaxies. Galaxy interactions have a secondary effect on pre-existing bars, typically accelerating their rotation, but we find no systematic difference between the pattern speeds of bars formed by interactions when compared to those formed in isolation.
