Specific star formation rate (sSFR) vs. redshift for the entire VLA/24 μm sample (grey dots) and for the radio-excess sources, divided into their three IR categories: IR AGN (red squares), IR SFG (blue circles) and passive systems (asterisks). The four sources plotted at the bottom (with a symbolic value of sSFR = 0.001 Gy^-1) are the four IR AGN for which the SFR could not be estimated (see Sect. 4.3). The tracks in the plot show the sSFR evolution with redshift for main sequence star-forming galaxies (MS; solid line) and for starburst galaxies (SB; dotted line) from Elbaz et al. (2011). The radio-excess sources have typically lower star formation than the star-forming galaxy population detected at 24 μm.