GOODS-Herschel: identification of the individual galaxies responsible for the 80-290 μm cosmic infrared background

Aims. We propose a new method of pushing Herschel to its faintest detection limits using universal trends in the redshift evolution of the far infrared over 24 mu m colours in the well-sampled GOODS-North field. An extension to other fields with less multi-wavelength information is presented. This method is applied here to raise the contribution of individually detected Herschel sources to the cosmic infrared background (CIRB) by a factor 5 close to its peak at 250 mu m and more than 3 in the 350 and 500 mu m bands. Methods. We produce realistic mock Herschel images of the deep PACS and SPIRE images of the GOODS-North field from the GOODS-Herschel key program and use them to quantify the confusion noise at the position of individual sources, i.e., estimate a local confusion noise. Two methods are used to identify sources with reliable photometric accuracy extracted using 24 mu m prior positions. The clean index (CI), previously defined but validated here with simulations, which measures the presence of bright 24 mu m neighbours and the photometric accuracy index (PAI) directly extracted from the mock Herschel images. Results. Both methods converge to comparable depths and fractions of the CIRB resolved into sources individually detected with Herschel. After correction for completeness, thanks to our mock Herschel images, individually detected sources make up as much as 54% and 60% of the CIRB in the PACS bands down to 1.1 mJy at 100 mu m and 2.2 mJy at 160 mu m and 55, 33, and 13% of the CIRB in the SPIRE bands down to 2.5, 5, and 9 mJy at 250 mu m, 350 mu m, and 500 mu m, respectively. The latter depths improve the detection limits of Herschel by factors of 5 at 250 mu m, and 3 at 350 mu m and 500 mu m as compared to the standard confusion limit. Interestingly, the dominant contributors to the CIRB in all Herschel bands appear to be distant siblings of the Milky Way (z similar to 0.96 for lambda < 300 mu m) with a stellar mass of M-star similar to 9 x 10(10) M-circle dot.