THE ROTATION OF THE GALAXY WITHIN THE SOLAR CIRCLE

A rotation curve for the Galaxy within the solar circle was derived using data from the fourth Galactic quadrant. The data were collected as a part of the Deep CO Survey of the Southern Milky Way. The observations are consistent with a picture in which the Galaxy rotates with a circular velocity of 209 ± 2 km s-1 between galactocentric distances 0.24 R⊙ and 1.0 R⊙. Clouds associated with a part of the Carina spiral arm (280° < l < 310°) exhibit an average rotation velocity 12 km s-1 higher than expected, implying an apparent anomalous motion. An excess in velocity of approximately the same magnitude observed at the tangent direction of the Centaurus arm (310° < l < 312°) is attributed to streaming and internal motions of large molecular complexes. Similar phenomena found in the Sagittarius and Scutum arms by northern observers strongly support the hypothesis that Carina is the continuation of the Sagittarius arm and Centaurus is that of the Scutum arm. The statistical dispersion of the terminal velocities, after removing the excess velocity associated with part of Carina and with the Centaurus tangent direction, has an rms value of 3.9 km s-1, which can be considered an upper bound of the cloud-cloud motions. We compare our data with southern H I observations and show that both tracers follow the same kinematics.