Aims. We quantify the contributions of 24 µm galaxies to the Far-Infrared (FIR) Background at 70 and 160 µm. We provide new estimates of the Cosmic Infrared Background (CIB), and compare it with the Cosmic Optical Background (COB). Methods. Using Spitzer data at 24, 70 and 160 µm in three deep fields, we stacked more than 19000 MIPS 24 µm sources with S 24 ≥ 60 µJy at 70 and 160 µm, and measured the resulting FIR flux densities.Results. This method allows a gain up to one order of magnitude in depth in the FIR. We find that the Mid-Infrared (MIR) 24 µm selected sources contribute to more than 70% of the Cosmic Infrared Background (CIB) at 70 and 160 µm. This is the first direct measurement of the contribution of MIR-selected galaxies to the FIR CIB. Galaxies contributing the most to the total CIB are thus z ∼ 1 luminous infrared galaxies, which have intermediate stellar masses. We estimate that the CIB will be resolved at 0.9 mJy at 70 and 3 mJy at 160 µm. By combining the extrapolation of the 24 µm source counts below analysis, we obtain lower limits of 7.1 ± 1.0 and 13.4 ± 1.7 nW m −2 sr −1 for the CIB at 70 and 160 µm, respectively. Conclusions. The MIPS surveys have resolved more than three quarters of the MIR and FIR CIB. By carefully integrating the Extragalactic Background Light (EBL) SED, we also find that the CIB has the same brightness as the COB, around 24 nW m −2 sr −1 . The EBL is produced on average by 115 infrared photons for one visible photon. Finally, the galaxy formation and evolution processes emitted a brightness equivalent to 5% of the primordial electromagnetic background (CMB).

We report the detection of correlated anisotropies in the Cosmic Far-Infrared Background at 160 µm. We measure the power spectrum in the Spitzer/SWIRE Lockman Hole field. It reveals unambiguously a strong excess above cirrus and Poisson contributions, at spatial scales between 5 and 30 arcminutes, interpreted as the signature of infrared galaxy clustering. Using our model of infrared galaxy evolution we derive a linear bias b = 1.74 ± 0.16. It is a factor 2 higher than the bias measured for the local IRAS galaxies. Our model indicates that galaxies dominating the 160 µm correlated anisotropies are at z ∼ 1. This implies that infrared galaxies at high redshifts are biased tracers of mass, unlike in the local Universe.