Fractional contribution to 3 GHz flux from free-free emission (top) and synchrotron emission (middle) as a function of redshift, assuming 10, 20, 30, and 40% contributions of free-free emission at 1.4 GHz rest-frame frequency (see legend in bottom panel). The bottom panel shows the power-law evolution of q_TIR determined in Sect. 3.1 (solid line), and the corrected evolution when the free-free emission contribution is properly taken into account.