OUTFLOW AND RADIATION CONES IN THE NARROW-LINE REGION OF NGC-4151

Emission-line profiles from various positions between 2″ and 6″ angular distance from the nucleus of NGC 4151 are utilized to describe the velocity field in the spatially resolvable part of the narrow-line region (NLR) of this galaxy. Half-peak level positions of the lines measured in rings at 2″ and 4″ nuclear distance show a sinusoidal behavior with position angle reminiscent of a rotating disk which is tilted and blueshifted relative to the main galactic plane of NGC 4151. However, although appealing, simple single-disk models are incompatible with the line shapes. Either flat-topped or two-component profiles are observed in the SW and in part of the NE narrow-line region. Arguments are presented which lead to a scenario consisting of normal galactic rotation combined with two outflow cones in the NE and SW. The SW cone extends at least from P.A. 180° to 300° corresponding to ∼400 pc. A discussion of the cloud stability suggests that a large part of the outflowing material is distributed over a giant shell which could be either driven by a wind or an expanding radio plasmon. The hot wind cavity accounts for the escape route of the recently discovered UV radiation beam in the SW. A faint northeastern 60° wide cone of [O III]/Hα enhancement is traced back to UV radiation penetrating through the NE bubble. The elongation of the narrow-line region is probably caused by the outflow. If this model proposed for NGC 4151 is generally applicable, the correlations between either UV beam or elongation with the radio axis found for a fair sample of galaxies suggest that the Seyfert radio sources are aligned with the main outflow directions.