Smoothed particle hydrodynamic simulations of galactic gaseous disk with bar: Distribution and kinematic structure of molecular clouds toward the galactic center

We have performed smoothed particle hydrodynamic (SPH) simulations to study the response of molecular clouds in the Galactic disk to a rotating bar an d their subsequent evolution in the Galactic center (GC) region. The Galact ic potential in our models is contributed by three axisymmetric components (massive halo, exponential disk, compact bulge) and a nonaxisymmetric bar. These components are assumed to be invariant in time in the frame corotatin g with the bar. Some noticeable features such as an elliptical outer ring, spiral arms, a gas-depletion region, and a central concentration have been developed due to the influence of the bar. The rotating bar induces noncirc ular motions of the SPH particles, but hydrodynamic collisions tend to supp ress the random components of the velocity. The velocity held of the SPH pa rticles is consistent with the kinematics of molecular clouds observed in H CN (1-0) transition; these clouds are thought to be very dense clouds. Howe ver, the longitude-velocity (l-v) diagram of the clouds traced by CO is qui te different from that of our SPH simulation, being more similar to that ob tained from simulations using collisionless particles. The I-v diagram of a mixture of collisional and collisionless particles gives better reproducti on of the kinematic structures of the GC clouds observed in the CO line. Th e fact that the kinematics of HCN clouds can be reproduced by the SPH parti cles suggests that the dense clouds in the GC are formed via cloud collisio ns induced by the rotating bar.