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The inner regions of barred galaxies contain substructures such as off-axis shocks, nuclear rings, and nuclear spirals. These substructure may affect star formation, and control the activity of a central black hole (BH) by determining the mass inflow rate. We investigate the formation and properties of such substructures using high-resolution, grid-based hydrodynamic simulations. The gaseous medium is assumed to be infinitesimally-thin, isothermal, and non-self-gravitating. The stars and dark matter are represented by a static gravitational potential with four components: a stellar disk, the bulge, a central BH, and the bar. To investigate various galactic environments, we vary the gas sound speed c_s as well as the mass of the central BH M_BH. Once the flow has reached a quasi-steady state, off-axis shocks tend to move closer to the bar major axis as c_s increases. Nuclear rings shrink in size with increasing c_s, but are independent of M_BH, suggesting that ring position is not determined by the Lindblad resonances. Rings in low-c_s models are narrow since they are occupied largely by gas on x2-orbits and well decoupled from nuclear spirals, while they become broad because of large thermal perturbations in high-c_s models. Nuclear spirals persist only when either c_s is small or M_BH is large; they would otherwise be destroyed completely by the ring material on eccentric orbits. The shape and strength of nuclear spirals depend sensitively on c_s and M_BH such that they are leading if both c_s and M_BH are small, weak trailing if c_s is small and M_BH is large, and strong trailing if both c_s and M_BH are large. While the mass inflow rate toward the nucleus is quite small in low-c_s models because of the presence of a narrow nuclear ring, it becomes larger than 0.01 Msun/yr when c_s is large, providing a potential explanation of nuclear activity in Seyfert galaxies.
Barred galaxies are known to possess magnetic fields that may affect the properties of bar substructures such as dust lanes and nuclear rings. We use two-dimensional high-resolution magnetohydrodynamic (MHD) simulations to investigate the effects of
Optical red spectra of a set of 18 bright barred spiral galaxies are presented. The study is aimed at determining the local kinematics, and the physical conditions of ionized gas in the compact nucleus (inside a diameter of 5) and in the circumnuclea
The observed velocities of the gas in barred galaxies are a combination of the azimuthally-averaged circular velocity and non-circular motions, primarily caused by gas streaming along the bar. These non-circular flows must be accounted for before the
Dust lanes, nuclear rings, and nuclear spirals are typical gas structures in the inner region of barred galaxies. Their shapes and properties are linked to the physical parameters of the host galaxy. We use high-resolution hydrodynamical simulations
We present hydrodynamic simulations of gas clouds inflowing from the disk to a few hundred parsec region of the Milky Way. A gravitational potential is generated to include realistic Galactic structures by using thousands of multipole expansions that