RAPID GAS-SUPPLY TO A NUCLEAR REGION BY SELF-GRAVITATIONAL INSTABILITY IN A WEAK BARRED POTENTIAL

We study gas dynamics in a weak barred potential with 2D numerical simulations, taking into account self-gravity of gas in order to explain the mechanism of rapid gas inflow into the central region of a starburst galaxy. We assume that the gas is initially uniformly distributed inside the corotation radius of the weak barred potential and pursue the self-gravitational gas motion in the case that the inner Lindblad resonance (ILR) exists in this potential. Our numerical results show that, for an initial gas-to-stellar mass ratio greater than 10 per cent, a central elongated gas ring becomes unstable and collapses after gas accumulates to form the elongated gas ring near the ILR radius. In the first phase of this process of collapse, dense gas clumps are formed at both sides of the elongated ring and collide with each other in a highly elongated orbit. After frequent collisions, these gas clumps merge and finally form a central dense core. As a result, a large amount of gas is concentrated in the centre beyond the ILR radius in a dynamical time-scale after the ring formation. We give a rough criterion for the rapid inflow of gas caused by gravitational instability.