The Number-Flux Density Relation for Radio Sources away from the Galactic Plane

Abstract

Two new series of observations at a frequency of 178 Mc/s have been combined to derive the number-flux density ( N–S ) relation for radio sources situated at galactic latitudes > 20°. In order to investigate the possible errors which might be introduced by various instrumental selection effects, detailed investigations have been made both of the distribution in “surface brightness” of the sources, and of the extent to which radio sources occur in clusters. It is shown that neither effect introduces an important error in the observed number-flux density relation. The observations, when corrected for these effects, provide a plot of log N against log S which, over the range 100 > S > 2 × 10 ⁻²⁶ w.(c/s) ⁻¹ m ⁻² , may be approximated by a straight line of slope −1.80. If account is taken of the errors in the observations and uncertainties in the analysis it is concluded that the slope lies in the range −1.68 to −1.93.