Extragalactic Radio Background at 2.1 MHz

Abstract

SURVEYS of cosmic radio emission carried out at metre and decametre wavelengths with telescopes of low resolving power detect the galactic background, a small number of intense discrete sources, and an isotropic background contributed by the integrated emission from extragalactic sources which are too faint to be detected individually. The brightness of this extragalactic background has recently been estimated from a spectral analysis¹ of the total radio background at metre and decametre wavelengths, and from an analysis² of the distribution of the total background at 85 MHz. The results of these studies imply that the brightness temperature of the extragalactic background is in the range 250° to 400° K at 85 MHz. It is likely that the extragalactic sources which contribute to this background have a distribution of spectral indices similar to that found in samples of the more intense extragalactic sources³. In this case, the brightness of their integrated emission would increase with decreasing frequency more rapidly than the brightness of the galactic background; the extragalactic component would contribute a greater proportion of the total brightness of any given area of sky as the observing frequency is decreased.