Spectral energy distribution of a merger remnant with mass 1.3 × 10⁸ M_⊙, f_Edd = 0.51 and spin 0.90, residing in a galaxy with mass 1.4 × 10¹¹ M_⊙ at redshift 3.55. The top panel depicts the (unobscured) rest-frame luminosities while the bottom panel depicts the (obscured) observer-frame flux. The SED of the remnant BH is shown in the solid black and red lines for the fiducial and the brightening scenario, while the approximate UV and X-ray galaxy SED is shown in the blue dashed lines. The green arrows indicate approximately the instrumental sensitivities assumed in radio at 2 GHz (assuming a sensitivity of 0.4 μjy), in UV at 1500 Å (m_UV, lim = 31.3), and in the 0.5 − 2 keV band (F_X, lim = 10⁻¹⁷ erg s⁻¹).