The Structure of the Galaxy from Radio Observations

The appearance of our Galaxy at radio wavelengths can be described as follows: The Milky Way stands out as a bright band of emission, at both long and short wavelengths. Above 50 cm, radio emission from the rest of the sky can also be observed. The brightness distribution is highly irregular. It can be interpreted as being due to the following sources: 1) Emission from ionized gas in the galactic plane, prominent at short wavelengths. 2) Synchrotron emission from the galactic disk and the Halo, prominent at long wavelengths. It is proposed that the sources of this nonthermal emission are clouds of relativistic particles and magnetic fields, possibly supernova remnants, distributed through the spiral arms and up to some distance from the galactic plane. The 21-cm line emitted by neutral hydrogen permits the astronomer to obtain a picture of the spiral structure and to study the motions of both the gas and the Galaxy as a whole. The galactic center and its surroundings poses a problem in itself, showing structure remarkable in both the continuum emission and in the neutral hydrogen distribution. Its structure suggests the possibility of an explosion of the galactic nucleus in the past.