Galaxy formation physics behind bar formation: A view from cosmological hydrodynamical simulations

We present a suite of zoom-in cosmological simulations of Milky Way-like galaxies with a prominent disc component and a strong bar in their centre based on a subsample of barred galaxies from the TNG50 magneto-hydrodynamic simulation. We modified the physical models that regulate star formation, namely, the supernova feedback and black hole quasar feedback, in order to examine how they affect disc and bar formation. We find that independent of the feedback prescriptions, all galaxies show a similar morphology, which is dominant in comparison with the bulge mass. The black hole quasar feedback models used in this study do not affect bar formation, although they can affect the bar strength and length. The energy released by the supernovae causes a delay in the time of bar formation, and in models with the strongest feedback, galaxies form stable discs against bar formation. This could be expected since supernova feedback influences disc and bulge assembly and results in discs with a lower mass content, radial velocity dispersion, and a larger size as the supernova feedback strength increases. We studied disc stability using three bar instability criteria proposed in the literature. We find that galaxies with varied supernovae and black hole quasar feedback satisfy these criteria at the moment of bar formation except in extreme cases where the galaxy lacks or has weak supernova feedback. In these models, two of the three criteria fail to forecast the existence (or absence) of a bar, probably because they do not account for the influence of a massive compact bulge. Our findings provide insights into the physical processes behind bar formation and highlight the importance of additional conditions other than a massive compact disc that promote bar formation.