Synthetic F814W photometry measured by determining from different values of ξ (Eq. (1)) is indicated by the blue points. The solid black line represents the F814W flux in the HST ACS frame. The 1σ range for the HST measurement is shaded grey. The red hatching indicates the hard lower limit on the measured F814W flux imposed by the X-shooter spectrum. The vertical red line indicates the resulting upper limit on ξ.