GASEOUS STRUCTURES IN BARRED GALAXIES: EFFECTS OF THE BAR STRENGTH

Using hydrodynamic simulations, we investigate the physical properties of gaseous substructures in barred galaxies and their relationships with the bar strength. The gaseous medium is assumed to be isothermal and unmagnetized. The bar potential is modeled as a Ferrers prolate with index n. To explore situations with differing bar strength, we vary the bar mass fbar relative to the spheroidal component as well as its aspect ratio R. We derive expressions as functions of fbar and R for the bar strength Qb and the radius r(Qb ) where the maximum bar torque occurs. When applied to observations, these expressions suggest that bars in real galaxies are most likely to have fbar ∼ 0.25-0.50 and n ∼< 1. Dust lanes approximately follow one of the x1-orbits and tend to be straighter under a stronger and more elongated bar, but are insensitive to the presence of self-gravity. A nuclear ring of a conventional x2 type forms only when the bar is not so massive or elongated. The radius of an x2-type ring is generally smaller than the inner Lindblad resonance, decreases systematically with increasing Qb , and is slightly larger when self-gravity is included. This is evidence that the ring position is not determined by the resonance, but instead by the amount of angular momentum loss at dust-lane shocks. Nuclear spirals exist only when the ring is of the x2 type and is sufficiently large in size. Unlike the other features, nuclear spirals are transient in that they start out being tightly wound and weak, and then, due to the nonlinear effect, unwind and become stronger until they turn into shocks, with an unwinding rate that is higher for larger Qb . The mass inflow rate to the galaxy center is found to be less than 0.01 M☉ yr–1 for models with Qb ∼< 0.2, while becoming larger than 0.1 M☉ yr–1 when Qb ∼> 0.2 and self-gravity is included.