Neutral hydrogen in nearby spiral galaxies holes and high velocity clouds

In this thesis we have investigated the neutral hydrogen distributions and kinematics of three nearby, face-on spiral galaxies: M 101, NGC 6946 and NGC 628. In particular, we have searched for holes and high velocity gas. The results obtained here throw new light on the processes taking place in the disks of spiral galaxies and on the disk - halo connection. We have also compared our observations with those of other nearby face-on and edge-on galaxies. ...