Left: distribution of FIR-radio flux ratio (q) for all of the sources in the VLA/24 μm sample (458 sources, excluding the upper limits; see Sect. 3.2); the blue Gaussian profile represents the best fit to the peak (q_mean = 2.21 ± 0.18), while the red dashed Gaussian is the q distribution found by Helou et al. (1985) for local starburst galaxies. The vertical line indicates the separation we assumed to select our radio-excess sources, q = 1.68, corresponding to 3σ from the peak (2σ when include radio upper limits). Right: FIR-radio flux ratio (q) as a function of redshift for all of the VLA/24 μm sources; the radio-excess sources have q < 1.68 (dot-dashed line); the solid horizontal line represents the average q value for the “radio-normal” sources (q = 2.21) and the shaded region indicates the ± 1σ error from this average. The radio-excess sources identified by Donley et al. (2005) are plotted as crosses (see Sect. 3.3). The binned q average for the “radio-normal” sources, in three redshift bins, is also shown as black circles; we found no significant evidence of evolution of the FIR-radio correlation out to z = 3.