IR SED modelling for IFRS at redshift z = 4, using the FIR flux density upper limits (red arrows) measured in this work. The total (black solid line) IR emission is composed of an AGN component (red dotted line) and a SB component (blue dashed line). The maximum model represents an upper limit on the IR emission of IFRS and is defined by the highest IR flux which is in agreement with all available flux density upper limits.