INTERMEDIATE-VELOCITY GAS IN THE NORTHERN GALACTIC HEMISPHERE - H-I STUDIES

This paper presents a study of the kinematics of intermediate negative velocity (similar to -40 km s(-1) > upsilon > -100 km s(-1)) neutral hydrogen toward the north Galactic pole using data from the Bell Labor atories 21 cm sky survey. The majority of the intermediate-velocity ga s is contained in three large coherent features covering nearly a thir d of the northern Galactic hemisphere. Contour plots of the emission a nd position-velocity diagrams reveal coherent velocity patterns spanni ng velocities from -100 km s(-1) to -20 km s(-1), and extending nearly 100 degrees across the sky. A few high-velocity cloud complexes appea r to be kinematically related to the intermediate-velocity gas; a clea r relationship between low-velocity (\upsilon\ < 20 km s(-1)) gas and intermediate velocity features is not apparent from the data. Distance estimates derived from absorption-line data by several. authors are c orrelated with the H I features to determine the masses of the interme diate-velocity gas features. The morphology, kinematics, distances, an d masses are used to evaluate models for the origin of the intermediat e-velocity gas, and three broad classes, infall, galactic fountains, a nd superbubbles, are found to be potentially viable.