Nuclear rings and mass inflow in hydrodynamic simulations of barred galaxies

We study the gas dynamics in barred galaxies using time-dependent hydrodynamic simulations. To achieve high resolution near the galaxy's center, the simulations are performed in cylindrical coordinates using a non-uniform radial grid. The gravitational potential of the bar is assumed to be time-independent and is modeled using a Ferrers ellipsoid. We find that the gas flow evolves to a quasi-steady state in roughly five bar orbits, and the general features of this steady state are similar to previous studies. However, we also find that if the gravitational potential has two inner Lindblad resonances, and if along the major and minor axes the extremum of the Ω - κ/2 curve between these resonances is at the same radial position, then the gas flow forms a dense nuclear ring located at the position of the extremum, or approximately 1 kpc for the models studied here. These two requirements are met by most models which have low axial ratio, i.e., thick bars. We study the development, evolution, and properties of the nuclear rings observed in our simulations in detail. We also study the effect of the bar on mass inflow into the nucleus of the galaxy. We find this inflow is highest for models with high axial ratio, i.e., thin, bars (which do not produce nuclear rings), where we find mass inflows of 0.25 M _⊙ yr^-1 into the inner 0.1 kpc.