Radio evidence for mass outflow in the Milky Way and external galaxies

Radio observations, particularly in the lambda21 cm line of neutral hydrogen, show that there are substantial non-circular motions in the Milky Way gas which indicate that gas is flowing outwards. Synchrotron emission from the central regions of the Milky Way provides evidence for substantial energy release. A large amount of gas has been deposited in the outer regions of the Milky Way in the form of intermediate velocity clouds and high velocity clouds. Mass outflow is seen in the broad-line and the narrow (forbidden) line regions in Seyfert galaxies. Expanding structures 1 to 5 kpc from the centre are in a number of such galaxies. Further evidence for energy release in the central regions comes from the recent discovery of radio jet-like objects in the centres of Seyfert galaxies. The subject is discussed under the headings: mass outflow from the Galactic centre; H I data relevant to the Galactic halo; ejection of matter from ordinary galaxies. (U.K.)