A far-infrared view of the Lockman hole from ISOPHOT

An important advance in the knowledge of the nature of galaxies is possible only using mid- and far-infrared data. In particular, the deep and extended surveys performed by the satellite ISO are suited for this kind of study. We present our preliminary results of the analysis of the PHOT 90mum data in the Lockman Hole with a recently developed technique (Lari et al. 2001). The survey covers an area of 40'x40', and is complementary to the shallow survey in the mid-infrared by ISOCAM. We are able to detect 36 sources down to a flux of similar to20 mJy. In particular, we discuss the cross-correlations between the far- and the mid- infrared sources. For the sample of sources detected in both IR bands, it becomes possible to study in detail the SEDs exploiting optical data (photometry in several bands and spectroscopy).