Left: Normalised FeI emission spectrum emerging from the dayside atmosphere of KELT-9 b as modelled with petitRADTRANS. Middle: Adopted T-p profile used for generating the emission template spectrum. Right: S/N map of FeI thermal emission from KELT-9 b’s dayside atmosphere. The signal peaks with a S/N of 5.2 after three consecutive SYSREM iterations. We indicate the coordinates of the strongest signal with the dashed white lines. Cross-sections of the S/N peak are shown in the horizontal and vertical panels.