We present a study of high-resolution long-slit spectra of the NLR of NGC 4151 and NGC 1068 obtained with the STIS aboard the HST. The spectra were retrieved from the MAST and were obtained from five and seven orbits of HST time resulting in five and seven parallel slit configurations at position angles of 52 degrees and 38 degrees for NGC 4151 and NGC 1068 respectively. The spectra have a spatial resolution of 0.2 arcsec across and 0.1 arcsec along each slit. Observations of [OIII] emissions from the NLR were made using the medium resolution G430M grating aboard HST. The spectral resolving power of the grating, which is about 9000, resulted in the detection of multiple kinematic components of the [OIII] emission line gas along each slit. Radial velocities of the components were measured using a Gaussian fitting procedure.
Biconical outflow models were generated to match the data and for comparison to previous models done with lower dispersion observations. The general trend is an increase in radial velocity roughly proportional to distance from the nucleus followed by a linear decrease after roughly 100 pc, similar to that seen in other Seyfert galaxies, indicating common acceleration/deceleration mechanisms. The FWHM of the emission lines reaches a maximum of 1000 km/s near the nucleus, and generally decreases with increasing distance to about 100 km/s in the extended narrow-line region (ENLR), starting at about 400 pc from the nucleus. In addition to the bright emission knots, which generally fit our model, there are faint high velocity clouds which do not fit the biconical outflow pattern of our kinematic model.
A comparison of our observations with high-resolution radio maps shows that the kinematics of the faint NLR clouds may be affected by the radio lobes that comprise the inner jet. However, the bright NLR clouds show a smooth transition across the radio knots in radial velocity and velocity dispersion plots and remain essentially undisturbed in their vicinity, indicating that the radio jet is not the principal driving force on the outflowing NLR clouds.