The effect of the self-gravity of gas on gas fueling in a barred galaxy with a supermassive black hole

In our previous paper, we showed that a gas disk in the nuclear region of a barred galaxy that contains a central supermassive black hole (SMBH) rapidly evolves into a nuclear gas ring because of an additional inner Lindblad resonance caused by the SMBH. In this paper, we investigate the fate of the gas ring, which involves the self-gravity of gas, using two-dimensional hydrodynamical simulations. We find that the gas ring becomes gravitationally unstable for the surface density of the gas above a critical value and fragments into several gas clumps. Some denser clumps increase their mass via the accretion of the surrounding gas and collisions with other clumps, and finally a very massive gas clump (M similar to 10(7) M.) is formed. Because of the torque from the massive clump, a part of the gas in the ring loses its angular momentum and falls into the galactic center. As a result, a nuclear gas disk (R similar to 50 pc) is formed around the SMBH. The accretion rate for R < 50 pc reaches about 0.1 M. yr(-1) for 3.5 x 10(7) yr. At the final phase of the bar-driven fueling, self-gravity is crucial for the angular momentum transfer of the gas. This is a new mechanism for gas fueling to the vicinity of the SMBH.