Galactlc bars are thlcker than Inner parts of gas dlsks. Therefore
gas flow Into theback side of bars, relatlve to the dlrectlon of dlsc
rotation, Thls Idea, based on the equlllbrium condltlon for galactlc rotating subsystems Is used to Interprete forbldden line emlsslon In bar regione vhere gas Inflow supersonic.
The suggested interpretation of the phenomenon of dlfferent velocity fields in the linea of dlfferent excltetion first discovered in the Seyfert galaxy Mkn 744 • NGC 3786 is now checked in the case of another Seyfert NGC 1068. .The appllcabillty Is controled from the Inferences concemlng the sense of rotation of spiral arms In the galaxies. In both cases these agree wlth the earlier results obtalned from Independent methods t the arms In NGC 1068 are trailling, while in NGC 3786 they are leadlng. One of manifestations of the shock back along the front slde of bars Is the occurence of stralght dust lanes along the front aide. Applications of the method
to other observational problems are discussed.
Recent observations show a dip on the rotation curve for most of
spiral galaxies,Theoretically, it implies that spiral density waves must be induced by shear instabilities,Calculations prove that the observed amount of gas In galactic disks (10% for the Galaxy) is sufficient to develop the hydrodynamical Instability in gas subsystems. As surface density perturbations of shallow water and
galactic gas disks are described by the same equations, experiments with shallow water rotating slmilar to galactic disks have been made, In stationary stages of rotation stationary spiral pattems occur. The number of arms depends on the profile of rotation curve, in agreement with theoretical results, Different rotation parameters lead to different structures: the circular mode, one-, two-, ... , eight-armed spirals. Branching of the spirals is observed when rotation parameters change,which suggests that the spiral branching in several galaxies comes from their
non-stationary rotation. Anticyclonic vortices are observed between the arms, Azimuthal averaging of the surface density, gives a good fit for the galaxy: minlmum of before the molecular ring, for realistic profiles of shallow water rotation the spirals are trailing, But they happen to lead for opposite directions of rotation of inner and outer
regions, It may explain the leading spirals in galaxies whose spin is opposite either to that oft.blose companions or to the vector of orbital momentum of the pairs. Numerical computations confirm the theoretical and experimental results.They also show a formation like a "molecular ring". Preliminary observational data agree with these results.