Source counts at 90 micron with the European Large Area ISO Survey (ELAIS)

We present results from the European Large Area ISO Survey (ELAIS) at 90 micron. With about 11.6 deg2 the survey is the largest area covered by ISO in a single programme and is 1.5 order of magnitude deeper than the IRAS 100 micron survey. Differential number counts are presented and show an excess of a factor up to 3.5 above the no-evolution model prediction at the faintest end of the survey. This confirms the strong evolution detected at shorter(15 micron) and longer (170 micron) wavelength in other ISO surveys. Comparison with several recent evolutionary models show that the best agreement with the observations is found for the model of Guiderdoni et al. (2001) which incorporates a heavily-extinguished population of galaxies.