Kinematic Disturbances in Optical Rotation Curves among 89 Virgo Disk Galaxies

Abstract

For 89 galaxies, mostly spirals, in the Virgo cluster region, we have obtained optical long-slit major axis spectra of the ionized gas. We find: (1) One-half of the Virgo galaxies we observed have regular rotation patterns, while the other 50% exhibit kinematic disturbances ranging from mild to major. Velocity complexities are generally consistent with those resulting from tidal encounters or accretion events. Since kinematic disturbances are expected to fade within ~10^9 years, many Virgo galaxies have experienced several significant kinematic disturbances during their lifetimes. (2) A few Virgo galaxies have ionized gas of limited extent, with velocities exceptionally low for their luminosities. In these galaxies the gas must be not rotationally supported. (3) There is a remarkable difference in the distribution of galaxy systemic velocity for galaxies with Regular rotation curves and galaxies with Disturbed rotation curves. Galaxies with regular rotation patterns show a flat distribution with systemic velocity, while galaxies with disturbed kinematics have a Gaussian distribution very similar to that for the elliptical galaxies in Virgo. This suggests that spirals with disturbed kinematics are preferentially on radial orbits, which bring them to the cluster core, where tidal interactions are strong and/or more common. These interactions may alter the morphology of the galaxy, and may also play a role in driving the Virgo cluster toward dynamical equilibrium.