GOODS-$Herschel$: identification of the individual galaxies responsible
  for the 80-290$\mu$m cosmic infrared background
  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$\mu$m and 500$\mu$m bands. 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. 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$$\sim$0.96 for $\lambda$$<$300$\mu$m) with a stellar mass
of $M_{\star}$$\sim$9$\times$10$^{10}$M$_{\odot}$.
