The Extragalactic Background and Its Fluctuations in the Far-Infrared Wavelengths

International audienceA Cosmic Far-InfraRed Background (CFIRB) has long been predicted that would trace the initial phases of galaxy formation. It has been first detected by [1] using COBE data and has been later confirmed by several recent studies [2], [3], [4]. I will present a new determination of the CFIRB that uses for the first time, in addition to COBE data, two independent gas tracers: the HI survey of Leiden/Dwingeloo [5] and the WHAM Hα survey [6]. We will see that the CFIRB above 100 µm is now very well constrained. The next step is to see if we can detect its fluctuations. To search for the CFIRB fluctuations, we have used the FIRBACK observations. FIRBACK is a deep cosmological survey conducted at 170µm with ISOPHOT [7]. We show that the emission of unresolved extra-galactic sources clearly dominates, at arc-minute scales, the background fluctuations in the lowest galactic emission regions. This is the first detection of the CFIRB fluctuations