of sources in 7C, compared to a random blank field, per mass bin.[]{data-label="fig:passivefraction"}](passive_fraction_mass_1arcmin.pdf){width="\columnwidth"}

Passive fraction as a function of mass
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The quiescent fraction is a strong function of $J$ band magnitude. As shown in the bottom panel of Figure \[fig:CMD\], the quiescent fraction gradually rises with decreasing magnitude. At $J<22.5$mag the fraction of quiescent galaxies in the protocluster rises to $>80$%, double the field fraction.

The $[4.5]$ flux provides a better correlation with stellar mass than the $J$ flux, and is nearly independent of galaxy type. Using galaxies with known stellar masses (from full SED-fitting) in the UDS [@Mortlock2013], we convert the \[4.5\] magnitudes to stellar mass using $\log ( M_* / {\rm M}_{\odot} )= 22.53-0.57\times[4.5]$. This equation was derived empirically by fitting a line to the stellar masses and \[4.5\] magnitudes from the UDS, which was resampled to have the same $J\le 23.6$ quiescent fraction as 7C, i.e. $50\%$, to remove the slight dependence of this relation on galaxy type. This line has an intrinsic scatter of $0.2$dex. We use this equation to calculate the masses for 7C. We use a similar equation but for the full UDS with no resampling, to calculate the masses for the field. 