Resolved Spectroscopy of the Narrow-Line Region in NGC 1068: Kinematics of the Ionized Gas

We have determined the radial velocities of the [O III]-emitting gas in the inner narrow-line region of the Seyfert 2 galaxy NGC 1068, along a slit at position angle 202 deg, from STIS observations at a spatial resolution of 0.1" and a spectral resolving power of λ/Δλ~1000. We use these data to investigate the kinematics of the narrow-line region within 6" (~430 pc) of the nucleus. The emission-line knots show evidence for radial acceleration to a projected angular distance of 1.7" in most cases, followed by deceleration that approaches the systemic velocity at a projected distance of ~4". We find that a simple kinematic model of biconical radial outflow can match the general trend of observed radial velocities. In this model, the emitting material is evacuated along the bicone axis, and the axis is inclined 5 deg out of the plane of the sky. The acceleration of the emission-line clouds provides support for dynamical models that invoke radiation and/or wind pressure. We suggest that the deceleration of the clouds is due to their collision with a patchy and anistropically distributed ambient medium. Based on observations with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.