PACS-to-24 μm flux density ratio as a function of the PACS flux density inferred from the “blind” source catalogue cross-matched with the MIPS-24 μm catalogue. Shaded regions show the space density distribution of galaxies at 70 μm (top left), 100 μm (top right) and 160 μm (bottom) in the GOODS-S field. In this field, the MIPS 24 μm catalogue reaches a 3σ limit of 20 μJy, while the PACS-70, 100 and 160 μm data reach 3σ limits of 0.9, 0.6 and 1.3 mJy (vertical dotted black lines). The parameter spaces reachable by our prior source extraction method using the MIPS catalogue are located below the dashed black lines: PACS sources located above these lines will not be detected at 24 μm. Orange triangles, red circles, light blue squares and dark blue stars show the PACS-to-24 μm flux density ratios of galaxies with L_IR = 10^11.5 L_⊙ as predicted at different redshifts using the spectral energy distributions (SEDs) of normal (MS), starburst (SB) galaxies (Elbaz et al. 2011), IRAS 22491 (Berta 2005) and Arp220 (Silva et al. 1998), respectively. The right point of each track corresponds to z = 0.5, while other points correspond to increasing redshifts, with intervals of Δz = 0.5 (arrows indicate the path followed for increasing redshift). Predictions for galaxies with lower or higher infrared luminosities will correspond to a global vertical shift of these tracks towards lower or higher PACS flux densities, respectively. Most of the PACS population lies well within the limits of the parameter space reachable by our MIPS 24 μm catalogues, i.e., below the dashed lines.