Detection of the extra-Galactic background fluctuations at 170 $\mu m$

We have used the Marano1 field observations with ISOPHOT at 170 $\mu$m to search for the Cosmic Far-InfraRed Background fluctuations. This field is part of the FIRBACK project (Puget et al., 1999a). For the first time, fluctuations due to unresolved extra-Galactic sources are isolated. The emission of such sources clearly dominates, at arcminute scales, the background fluctuations in the lowest Galactic emission regions. The study presented here is based on a power spectrum analysis which allow to statistically separate each of the background components. With this analysis, we clearly show that we detect the CFIRB fluctuations