A classical approach to faint extragalactic source extraction from ISOCAM deep surveys. Application to the Hubble Deep Field

We have developed a general data reduction technique for ISOCAM data coming from various deep surveys of faint galaxies. In order to reach the fundamental limits of the camera (due to the background photon noise and the readout noise), we have devised several steps in the reduction processes that transform the raw data to a sky map which is then used for point source and sligthly extended source extraction. We show illustrative examples of our present scheme by using data taken from the publicly available Hubble Deep Field ISOCAM survey in order to demonstrate its characteristics. More than thirty sources down to the 60 (resp. 100) microJy level are clearly detected above 4 sigma at wavelengths of 7 (resp. 15) micron, the vast majority at 15 micron. A large fraction of these sources can be identified with visible objects of median magnitude 22 and K-band magnitude of 17.5 and redshifts between 0.5 and 1 (when available). A few very red objects could be at larger redshifts.