2007ApJ...663...71N

We describe our characterization of the kinematics of the emission-line gas in the nuclear regions of a complete sample of 21 nearby radio galaxies. We obtained data using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We show that the point-to-point variations are largest perpendicular to the disks and in nuclei where the organized motion is less pronounced, suggesting that motions are present from gas that has not settled into smooth rotation. We show that the velocity dispersion is not distributed as a function of inclination, and so likely arises from isotropic random motions in the gas. We find that the difference in mean velocities on either side of the nucleus does not vanish as the disks become face-on, suggesting there may be bulk motions of the gas disks. We show that the gas velocity dispersions are closely related to the stellar velocity dispersions, which has implications for black hole fueling and growth mechanisms. We show that significant motions digressing from a smooth thin disk configuration are ubiquitous, and even in those cases where the velocity profile of the emission-line gas appears smooth and uncomplicated there may be dynamical components of the system that are not explained by a thin Keplerian disk model, suggesting caution in the use of gas disk kinematics for the determination of black hole masses.