An investigation of galactic radiation in the radio spectrum

Abstract

An investigation of the distribution of the sources of galactic radiation at 64 Mcyc./sec. is described. Methods are discussed by which the characteristics of the receiving antenna were measured and by which the magnitude of the received galactic power was estimated by comparison with a reference signal of similar amplitude characteristics. The method of analysis of results is described in detail, with emphasis on the need for allowing for the finite width of the main cone of reception of signal power and for the sensitivity of the antenna to signal sources outside the main cone. The necessary corrections are effected by a method of successive approximations, and contours of the distribution of the signal source between declinations + 50° and — 30° are derived. The results are expressed in terms of power flux and also of effective aerial temperature. Possible sources of error are discussed and an accuracy better than 1.2 db. (30 %) is expected for the regions of highest radiation intensity. Reference is made to the fluctuations observed in the radiations coming from Cygnus. The correlation of the derived distribution of galactic radiations with other astronomical data is discussed with special reference to the galactic structure. It is shown that correlation with the near galactic structure, as indicated by the general distribution of visible sources of light, is not very good, but that a more satisfactory correlation is obtained with data which are believed to be characteristic of the structure of the galaxy as a whole. The bias to the south of the galactic circle shown by radiation sources in the vicinity of the galactic centre is especially significant. Various relevant astronomical data are collected together in the accompanying diagrams. The bearing of these correlations on the question of the nature of the source of radiation is examined. It is shown that they do not clearly favour any one theory, and that neither a simple theory in terms of a distributed source in interstellar gas nor one in terms of discrete centres of radiation analogous to sunspots appears adequate to account for the observed phenomena. It is suggested that sources of both types contribute to the observed radiation and that, in general, they must be very distant and associated with the main body of the galaxy.