The coronas of galaxies

Abstract

The instrumentation and results of observations of interstellar and intergalactic gases are reviewed, particularly for UV satellite data on the dynamics and composition of the galactic corona. Radio telescopes began the mapping of gas in the central galactic disk in the 1950's, using 21-cm readings to detect atomic hydrogen clouds 100,000 light years from the earth, i.e., across the total disk of the galaxy. The International UV Explorer satellite (IUE), operated jointly by NASA, ESA, and the British Science Research Council, launched in 1978 produced evidence indicating the presence of the galactic corona, which is hypothesized to exert sufficient pressure to keep galactic interstellar gas from dispersing into intergalactic space. The IUE carries a telescope and a spectrometer in addition to television cameras to transmit imagery to ground stations. Results of observations of the Magellanic Clouds have indicated that hot coronal gases are common to spiral and irregular galaxies.