Source Counts at High Spatial Densities From Pencil Beam Observations of Background Fluctuations

The Parkes 64-m telescope has been used at 2700 and 5000 MHz to determine frequency distributions of the spatial fluctuations in the background continuum. These distributions reflect the number–flux density relations for the weaker sources. The 2700 MHz results place constraints on this relation down to a flux density of ~ 1 mJy, corresponding to $$\sim2\,\times\,{10}^{5}$$ sources per steradian, or more than twice the spatial density reached in published aperture synthesis surveys. The very limited observations at 5000 MHz demonstrate the feasibility of the technique for determining the number-flux density relation at this frequency to ~ 10⁶ sources per steradian. Brief comparison is made between the relations derived here and the relations previously found at lower frequencies.