A new method to determine the sense of rotation of spiral arms in the barred galaxies

Galactic bars are thicker than inner parts of gas disks. Therefore, gas flows into the rear of bars, relative to the direction of disc rotation. This idea, based on the equilibrium condition for galactic rotating subsystems, is used to interpret forbidden line emission in bar regions where gas inflow is supersonic. The suggested interpretation of the phenomenon of different velocity fields in the line of different excitation first discovered in the Seyfert galaxy Mkn 744 = NGC 3786 is now checked in the case of another Seyfert NGC 1068. The applicability is controlled from the inferences concerning the sense of rotation of spiral arms in the galaxies. In both cases these agree with earlier results obtained from independent methods: the arms in NGC 1068 are trailing, while in NGC 3786 they are leading. One of manifestations of the shock back along the front side of bars is the occurrence of straight dust lanes along the front side. Applications of the method to other observational problems are discussed. (author). 3 figs., 13 refs