2 Radio observations

The Phoenix survey has been performed at 1.4GHz using the 6A configuration of the Australia Telescope Compact Array (ATCA). It is a mosaic of 30 pointing centres covering a $2^{\circ}$ diameter field centred at $\mathrm{RA}(2000)=01^{\mathrm h}~14^{\mathrm m}~12\hbox{$.\!\!^{\rm s}$ }16$ ; $\mathrm{Dec.}(2000)=-45^{\circ}~44'~8\hbox{$.\!\!^{\prime\prime}$ }0$. The final synthesised beam size is $\approx$8arcsec. Details of the observation, data reduction, source detection and catalogue generation are presented in Hopkins et al. (1998). A source is included in the sample if its peak flux density is 4$\sigma$ above the local rms and if it survives visual inspection. There are two sources of incompleteness in the catalogue, as with any peak flux density limited sample. The first is a result of the attenuation of the primary beam sensitivity away from a field centre. This effect has been minimised in the Phoenix survey by the mosaicing strategy used. The second is the fact that extended objects with a total flux density above the survey limit can be missed by a source detection algorithm which initially detects candidates based on their peak flux densities. These effects have been described in Hopkins et al. (1998). The catalogue is estimated to be $50\%$ complete to 0.3mJy, and $80\%$ complete to 0.4mJy. Therefore to minimise the effect of incompleteness when performing the correlation analysis, we restrict ourselves to a subsample containing all sources brighter than 0.4mJy.