Survey [UDS; @Hartley2013] as a control field. The IRAC fluxes in the UDS catalogue were deblended using the same method described above, using the resolved $K_s$ images to deblend sources [see @Hartley2013]. The UDS has $5\sigma$ depths of $i'=27.0$mag, $J=24.9$mag, $[3.6]=24.2$mag and $[4.5]=24.0$mag [@Furusawa2008; @Hartley2013]. We therefore use the same magnitude cuts for the UDS as for the C field. We do not consider Eddington bias due to the greater depth of the UDS, however we do not expect it to significantly affect our results, particularly regarding the fraction of the most massive galaxies in the cluster that are quiescent.

The UDS is a $K_s$-selected survey, whereas we use an F140W selection for C. Both selections are done in the infrared, and both are much deeper than our $J \le 23.6$mag selection so these methods are unlikely to differ greatly. They would only differ for extremely red sources with very faint F140W magnitudes and bright $K_s$ magnitudes. We have checked that the different selection methods do not affect our use of the UDS as a control sample by comparing number counts in the two fields as a function of $i'$, $J$, $[3.6]$ and $[4.5]$ magnitudes and find that they match 