Kinematics of molecular clouds. II - New data on nearby giant molecular clouds

The best currently available data on positions, distances, and velocities of giant molecular clouds within 3 kpc of the sun are analyzed to yield a one-dimensional rms cloud-to-cloud velocity dispersion of 7.8 +0.6, -0.5. Velocity dispersion is defined here as the root mean square of cloud peculiar velocities, a quantity which includes small-scale streaming. It is argued that this value for the velocity dispersion is pausible, based on examples of clouds whose velocities cannot be explained purely by galactic rotation. The mean motion of nearby molecular clouds is drifting by about 4 km/s with respect to the LSR.