As a pilot study for the first all–sky radio survey at short wavelengths , we have observed 1216 deg ^ { 2 } of the southern sky at 18 GHz ( 16 mm ) using a novel wide–band ( 3.4 GHz bandwidth ) analogue correlator on one baseline of the Australia Telescope Compact Array ( ATCA ) .
We scanned a region of sky between declination -71 ^ { \circ } and -59 ^ { \circ } with an rms noise level of 15 mJy .
Follow–up radio imaging of candidate sources above a 4 \sigma detection limit of 60 mJy resulted in 221 confirmed detections , for which we have measured accurate positions and flux densities .
For extragalactic sources , the survey is roughly 70 % complete at a flux density of 126 mJy and 95 % complete above 300 mJy .
Almost half the detected sources lie within a few degrees of the Galactic plane , but there are 123 sources with |b| > 5 ^ { \circ } which can be assumed to be extragalactic .
The differential source counts for extragalactic sources in the range 0.1 \hbox { Jy } \leq S _ { 18 { GHz } } \leq 3 \hbox { Jy } are well fitted by a relation of the form n ( S ) = 57 ( S / \hbox { Jy } ) ^ { -2.2 \pm 0.2 } \hbox { Jy } ^ { -1 } \hbox { sr } ^ { -1 } , in good agreement with the 15 GHz counts published by Taylor et al .
( 2001 ) and Waldram et al .
( 2003 ) .
Over 70 % of the extragalactic sources have a flat radio spectrum ( \alpha _ { 0.843 } ^ { 18 } > -0.5 , S _ { \nu } \propto \nu ^ { \alpha } ) , and 29 % have inverted radio spectra ( \alpha _ { 0.843 } ^ { 18 } > 0 ) .
The optical identification rate is high : 51 % of the extragalactic sources are identified with stellar objects ( candidate QSOs ) , 22 % with galaxies and only 27 % with faint optical objects or blank fields .