The European Large Area ISO Survey:: 90 micron number counts

The European Large Area ISO Survey (ELAIS) was the largest single Open Time project conducted by ISO, mapping an area of 12 square degrees at 15mum with ISOCAM and at 90mu with ISOPHOT. We first present the data analysis of the 90 mum survey. We show comparisons with model prediction for standard stars and with COBE/DIRBE for surface brightnesses of individual ELAIS fields and with the IRAS FSC catalog for 35 sources in common. The large number of rasters necessary to cover the wide ELAIS areas allows to compute a relative uncertainty for the calibration based on the FCS of typically 7%. From the comparison with standard stars model predictions, the absolute calibration is shown to be better than 15%. The survey is 1.5 order of magnitude deeper than the IRAS 100mum survey and is expected to provide constraints on the formation and evolution of galaxies. Finally, we present 90 mum number counts from a reliable subset of the detected sources. ELAIS number counts are compared to the evolutionary models of Guiderdoni (1998) and Rowan-Robinson (2001).