The FIRBACK ( Far Infrared BACKground ) survey is one of the deepest imaging surveys carried out at 170 \mu m with ISOPHOT onboard ISO , and is aimed at the study of the structure of the Cosmic Far Infrared Background .
This paper provides the analysis of resolved sources .
After a validated process of data reduction and calibration , we perform intensive simulations to optimize the source extraction , measure the confusion noise ( \sigma _ { c } = 45 mJy ) , and give the photometric and astrometric accuracies .
196 galaxies with flux S > 3 \sigma _ { c } are detected in the area of 3.89 square degrees .
Counts of sources with flux S > 4 \sigma _ { c } present a steep slope of 3.3 \pm 0.6 on a differential ” logN-logS ” plot between 180 and 500 mJy .
As a consequence , the confusion level is high and will impact dramatically on future IR deep surveys .
This strong evolution , compared with a slope of 2.5 from Euclidian geometry , is in line with models implying a strongly evolving Luminous Infrared Galaxy population .
The resolved sources account for less than 10 % of the Cosmic Infrared Background at 170 \mu m , which is expected to be resolved into sources in the 1 to 10 mJy range .