Gas inflow in barred galaxies: effects of secondary bars

We report results of high-resolution hydrodynamical simulations of gas flows in barred galaxies, with a focus on gas dynamics in the central kiloparsec. In a single bar with an inner Lindblad resonance, we find either near-circular motion of gas in the nuclear ring, or a spiral shock extending towards the galaxy centre, depending on the sound speed in the gas. From a simple model of a dynamically possible doubly barred galaxy with resonant coupling, we infer that the secondary bar is likely to end well inside its corotation. Such a bar cannot create shocks in the gas flow, and therefore will not reveal itself in colour maps through straight dust lanes: the gas flows induced by it are different from those caused by the rapidly rotating main bars. In particular, we find that secondary stellar bars are unlikely to increase the mass inflow rate into the galactic nucleus.