Pattern speed evolution of barred galaxies in TNG50

Context. Galactic bars are found in the majority of disc galaxies. They rotate nearly rigidly with an angular frequency called pattern speed. In idealised simulations, the bar pattern speed generally decreases with time due to dynamical friction exerted by the dark-matter halo, while cold gas can reduce or even reverse this trend. Aims. We want to understand how different galaxy properties affect the evolution of the bar pattern speed in more realistic situations, including ongoing star formation, mass infall, active galactic nucleus (AGN) feedback, and galaxy interactions. Methods. We traced the pattern-speed evolution of simulated bars in the TNG50-1 cosmological simulations. Results. Simulated bars with an initially high pattern speed and a subsequent rapid slowdown are more likely found in more massive galaxies. Lower mass galaxies, on the other hand, preferentially host bars that start at relatively low pattern speeds and retain the same value until the end of the simulation. More massive simulated barred galaxies are also more affected by the AGN-feedback model, which very efficiently removes the cold gas that could have prevented the slowdown. Conclusions. We find that bars grow and strengthen with slowdown, in agreement with higher resolution simulations. We find that strong correlations between the bar slowdown rate and galaxy mass weaken considerably when we use dimensionless measures to quantify the slowdown. In TNG50, the AGN-feedback prescription amplifies the mass dependence. Turned around, this provides an interesting statistic to constrain sub-grid physics by bar growth and slowdown.