well within the colour and magnitude cuts stated above.

Where we compare the properties of the cluster galaxies to the field, we use only those galaxies selected in the UDS which have photometric redshifts between $1.5<z<1.7$.[^3] This ensures we are comparing the cluster properties to those of the field at approximately the same redshift. For statistical subtraction (see below), we use the full UDS with no photometric redshift constraints.\

### Subtraction of field contaminants

Since we do not identify cluster members with spectra or photometric redshifts, we use statistical subtraction to derive the cluster galaxy properties. The fore- and background population is estimated from $\sim400$ random 0.9arcmin radius regions in the UDS, having applied the same colour and magnitude cuts as above. The field contribution is estimated from the median of these 400 regions and then subtracted from the corresponding number of galaxies around C. The uncertainty is the 1$\sigma$ standard deviation of the 400 field regions.

Redshift of 7C1753+6311 {#sec:spectrum}
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![The Keck/LRIS spectrum of 7C1753+6311 obtained on UT 2011 February 28 (smoothed with a boxcar average of 10Å for clarity). A single, high equivalent width emission line is detected at 9602Å which we identify as the \[\] $\lambda 