Comparison between the photometric monochromatic luminosities at 7.7 μm, νL_{ν photo} (7.7 μm), and at 3.5 μm, νL_{ν photo} (3.5 μm). The PAH galaxies are shown with one-sigma error bars in different colours for different redshift bins: blue, black, and red for the nearby, mid-z, and higher-z galaxies, respectively. SFR and stellar mass are estimated from νL_{ν photo} (7.7 μm) and νL_{ν photo} (3.5 μm), respectively, as explained in the text. A correlation between stellar mass and SFR for main sequence galaxies for z ∼ 0 SDSS sample (Elbaz et al. 2007) is indicated by a grey hatched area, showing one-sigma scatter around the best fit line (broken line). A diagonal dot-broken line for a fixed PAH-to-stellar luminosity ratio (log νL_{ν photo} (7.7 μm) = 0.50 + log νL_{ν photo} (3.5 μm)) is used to identify the PAH-enhanced population (on the lower right side of this line).