Spectroscopic evidence bearing on the distribution of gas in extra-galactic systems

Extract

Six years ago, in a joint paper with W. Baade, I presented certain spectrographic data bearing on the distribution and motions of gaseous masses in spiral nebulae. Since then progress in this special field has been unspectacular and relatively slow by conventional optical means, mainly because of the considerable faintness of the sources. Nevertheless, the optical data now seem sufficiently representative to warrant a review directed toward an eventual comparison of optical and radio results. For there can be little doubt that the new radio astronomy techniques give every indication of revolutionary new advances. Highly significant results have been obtained for the Magellanic Clouds, a beginning has been made in the local group spirals such as the Andromeda nebula, and it is reasonable to expect, as more powerful installations come into operation, that the nearer field and great cluster nebulae will come under detailed radio observation. But these matters have been considered at the recent Jodrell Bank symposium on radio astronomy, in Manchester. For this reason and because I am not a radio astronomer I shall proceed, without further discussion of these exciting new developments, to a description of the more prosaic optical data obtained from spectrographic observations.