ABSTRACT

Observational evidence for the existence of bars in the central parts of Seyfert galaxies Mkn 744, Mkn 573, and NGC 4151 is presented.

INTRODUCTION

Afanasiev (1981) investigated rotation curves of 28 Seyfert galaxies and found local maxima at distances 0.5–2 kpc from the centers in 20 objects. The rotation velocity declined with the increasing distance from the local maximum more rapidly than for the Keplerian law. This suggests a possibility of development of Kelvin-Helmholtz instability leading to essential turbulization of the circumnuclear disk (global gas instability in the disk) (Morozov 1979). Observed solid body rotation, from the center to the local maximum, indicates a possible presence of bars in the centers of Sy s.

GAS MOTION FEATURES IN THE BAR'S REGION

Gaseous disk in the region of the bar is thinner than the latter, has lower chaotic velocities and rotates faster than the bar Ωd > Ωb (Fridman 1987). If the radius R1, where the relative linear velocity ΔVR reaches the sound speed in the gaseous disk ΔVR = (Ωd – Ωb)R > Vs, is within the bar region (Rb), then a shock may arise for R1 < Rb. The shock front then will be observed on the rear side of the bar with respect to the direction of rotation, if the disk and the bar rotate in the same direction. Depending on the ΔVR value, either strong or weak shocks will be observed in the optical band (mainly in the forbidden lines) as linear structures.