Kinematic disturbances in optical rotation curves among 89 Virgo disk galaxies

For 89 galaxies, mostly spirals, in the Virgo Cluster region, we have obtai ned optical long-slit major-axis spectra of the ionized gas. We find the fo llowing: (1) One-half of the Virgo galaxies we observed have regular rotati on patterns, while the other half exhibit kinematic disturbances ranging fr om mild to major. Velocity complexities are generally consistent with those resulting from tidal encounters or accretion events. Since kinematic distu rbances are expected to fade within similar to 10(9) yr, many Virgo galaxie s have experienced several significant kinematic disturbances during their lifetimes. (2) There is no strong correlation of rotation curve complexity with Hubble type, with galaxy luminosity, with local galaxy density, or wit h H I deficiency. (3) A few Virgo galaxies have ionized gas of limited exte nt, with velocities exceptionally low for their luminosities. In these gala xies the gas must be not rotationally supported. (4) There is a remarkable difference in the distribution of galaxy systemic velocity for galaxies wit h regular rotation curves and galaxies with disturbed rotation curves. Gala xies with regular rotation patterns show a flat distribution with velocitie s ranging from V-0 = -300 km s(-1) to V-0 = +2500 km s(-1); galaxies with d isturbed kinematics have a Gaussian distribution that peaks at V-0 = +1172 +/- 100 km s(-1), close to the cluster mean velocity. This latter distribut ion is virtually identical to the distribution of systemic velocity for ell iptical galaxies in Virgo. However, disturbed galaxies are less concentrate d to the cluster core than are the ellipticals; those near the periphery ha ve velocities closer to the mean cluster velocity. Thus, spirals with distu rbed kinematics are preferentially on radial orbits, which bring them to th e denser core, where tidal interactions are strong and/or more common. Beca use they spend much time near apocenter, we observe them near the cluster p eriphery. Some may be falling into the core for the first time. These obser vations suggest that for a nonvirialized cluster like Virgo, galaxies may e ncounter either local (nearby galaxies) or global (cluster-related) interac tions. These interactions may alter the morphology of the galaxy and may al so play a role in driving the Virgo Cluster toward dynamical equilibrium.