Rettura et al. (in preparation). In comparison to radio galaxies surrounded by protoclusters typically reported in the literature [e.g. @Venemans2007; @Galametz2010a; @Hatch2011a], this is a relatively weak line emitter. We do not find any features at 4854Å and this wavelength does not correspond to any strong spectral features for our measured redshift. The feature noted in @Lacy1999 was therefore probably due to noise in their shallow data.

Cluster properties {#sec:results}
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A galaxy cluster at $z=1.58$
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Figure \[fig:density\] shows a density map of the field around C and ClG0218.3$-$0510, a well-studied cluster at $z=1.62$ [@Papovich2010; @Tanaka2010]. These maps were produced by measuring the number density of sources (selected using the colour and magnitude criteria described in Section \[sec:method\]) within 30arcsec radius apertures around each 5arcsec pixel. The UDS was mapped in the same way, and the mean and standard deviation of densities in the UDS were used to convert each number density value to a significance above the expected field density. The pixels in Figure \[fig:density\] are therefore correlated as each 5arcsec pixel indicates the overdensity within a 30arcsec radius aperture. Using the selection criteria defined in Section \[sec:method\], the peak overdensity around C is an $8.9\sigma$ significance of 