Selection limits introduced in the T_dust−L_IR parameter space by our deepest PACS observations, i.e., in GOODS-S-ultradeep. Red continuous lines are these selection limits at different redshifts using our PACS 5σ detection limits. Each line corresponds to the central redshift of our redshift bins, i.e., z = 0.25 (further left), z = 0.55, z = 0.85, z = 1.15, z = 1.55 and z = 2.05 (further right). The shaded area shows the local T_dust−L_IR relation found by Chapman et al. (2003), linearly extrapolated to 10¹³ L_⊙. Dot-dashed lines show the T_dust−L_IR relation inferred by Symeonidis et al. (2013) using a sample of high-redshift (i.e., 0.2 < z < 1.2) Herschel-detected galaxies. Dashed black lines show, for each redshift, the lowest infrared luminosities probed by our ultradeep PACS observations without any dust temperature biases and yet populated by star-forming galaxies.