KINEMATICS OF THE URSA-MAJOR MOLECULAR CLOUDS

We present a kinematic analysis of the atomic and molecular gas in the Ursa Major molecular clouds. The analysis is based on a new CO survey of the complex made with linear resolution of 0.05 pc and existing H I observations. The clouds lie in projection on an expanding shell of material known as the North Celestial Pole loop. The molecular structu re of the complex is dominated by several long (>5 pc) filaments, some of which are both extremely straight and extremely narrow (<0.2 pc ac ross). These filaments are enclosed in a sheath of neutral atomic hydr ogen that has a kinematic signature distinct from the surrounding atom ic gas. The tips of the filaments are regions of enhanced IRAS 12 and 25 mu m emission. We find an offset of up to 4 km s(-1) between the ce ntroid velocities of the CO and H I, a large-scale velocity gradient i n the gas of similar to 0.3 km s(-1) pc(-1), and a similar large-scale gradient in the H I line width. The CO velocity field follows a trend similar to the H I but is much less organized. A weak line width grad ient in the CO may also be present. We present a model in which the cl ouds lie near the surface of the expanding bubble and, after having in teracted with the bubble's wind, are now slowly ''sliding'' down the b ubble toward the Galactic plane. This model adequately accounts for th e atomic-molecular velocity offset, the velocity gradients, the line w idth gradient, and the IRAS colors.