Dynamical decoupling of nested bars: Self-gravitating gaseous nuclear bars

A substantial fraction of barred galaxies host additional nuclear bars that tumble with pattern speeds exceeding those of the large-scale (primary) stellar bars. We have investigated the mechanism of formation and dynamical decoupling in such nested bars that include gaseous (secondary) nuclear bars within the full-size galactic disks, hosting a double inner Lindblad resonance. Becoming increasingly massive and self-gravitating, the nuclear bars lose internal ( circulation) angular momentum to the primary bars and increase their strength. Developing chaos within these bars triggers a rapid gas collapse-bar contraction. During this time period, the secondary bar pattern speed Omega(s)similar toa(-1), where a stands for the bar size. As a result, Omega(s) increases dramatically until a new equilibrium is reached (if at all), while the gas specific angular momentum decreases-demonstrating the dynamical decoupling of nested bars. Viscosity, and therefore the gas presence, appears to be a necessary condition for the prograde decoupling of nested bars. This process maintains an inflow rate of similar to1 M-circle dot yr(-1) over similar to10(8) yr across the central 200 pc and has important implications for fueling the nuclear starbursts and active galactic nuclei.