[CDF99] F 4-2 , the SIMBAD biblio

We present the first results of a study of faint 12µm sources detected with the Infrared Space Observatory (ISO) in four deep, high galactic latitude fields. The sample includes 50 such sources in an area of 0.1 square degrees down to a 5σ flux limit of ∼500µJy. From optical identifications based on the US Naval Observatory (USNO) catalogue and analysis of the optical/IR colours and Digital Sky Survey (DSS) images, we conclude that 37 of these objects are galaxies and 13 are stars. We derive galaxy number counts and compare them with existing IRAS counts at 12µm, and with models of the 12µm source population. In particular, we find evidence for significant evolution in the galaxy population, with the no-evolution case excluded at the 3.5σ level. The stellar population is well matched by existing models. Two of the objects detected at 12µm are associated with known galaxies. One of these is an IRAS galaxy at z=0.11 with a luminosity of 10¹¹L_☉.