FIRBACK Source Counts and Cosmological Implications

FIRBACK is a one of the deepest survey performed at 170 μm with ISOPHOT onboard ISO, and is aimed at the study of the cosmic far infrared background sources. About 300 galaxies are detected in an area of four square degrees, and source counts present a strong slope of 2.2 of the integral ”logN-logS” plot, which cannot be due to the effect of the cosmological evolution if no K-correction is present. The resolved sources account for less that 10% of the Cosmic Infrared Backgound at 170 μm. In order to understand the nature of the sources contributing to the CIB, and to explain deep source counts at other wavelengths, we have developped a phenomenological model, which constrains in a simple way the luminosity function evolution with the redshift, and fits all the existing deep source counts from the mid-infrared to the submillimetre range.