The ATESP radio survey - III. Source counts

This paper is part of a series reporting the results of the ATESP radio survey obtained at 1.4 GHz with the Australia Telescope Compact Array. The survey consists of 16 radio mosaics with ∼ $8\arcsec \times 14\arcsec$ resolution and uniform sensitivity ($1 \sigma$ noise level ∼ 79 μ Jy) over the whole area of the ESO Slice Project redshift survey ( ∼ 26 sq. degr. at $\delta \sim -40\degr$). The ATESP survey has produced a catalogue of 2960 radio sources down to a flux limit ($6\sigma$) of ∼ 0.5 mJy. In this Paper we present the 1.4 GHz $\log N - \log S$ relation derived from the ATESP radio source catalogue. The possible causes of incompleteness at the faint end of the source counts are extensively discussed and their effects are quantified and corrected for. The ATESP counts are consistent with others reported in the literature, even though some significant discrepancies are present at low fluxes (below a few mJy). We investigate whether such discrepancies may be explained in terms of field-to-field anisotropies, considering the fact that all the existing sub-mJy surveys cover small areas of sky (from a fraction of square degree to a few square degrees). We stress that the ATESP survey, covering 26 sq. degr., provides the best determination of source counts available today in the flux range $0.7\la S_{1.4 \rm{GHz}}\la 2$ mJy.