The ELAIS Survey

Involved people at OAB: Ciliegi, Gruppioni, Mignoli, Pozzi.

ELAIS was the largest non serendipitous ISO field survey, utilizing 377 hours of the Open-Time programme. The project is a collaboration venture between 26 institutes from 11 countries. The survey covers around 13 sq.degree with observations in four bands covering much of the ISO wavelength window (6.7, 15, 90 and 175 micron) using both ISO-CAM and ISO-PHOT. During 1999, in collaboration with Francesca Pozzi (PhD student, University of Bologna) and Carlo Lari (Institute of Radio astronomy CNR, Bologna) the data reduction of the ISO-CAM data at 15 micron in a region of the sky of 2 2 degree called S1 has been performed. They used the data reduction software developed by Carlo Lari, which was especially designed to overcome the main problems affecting ISOCAM LW data and to detect faint sources. With this new reduction technique a complete sample of more than four hundred 15m sources brighter than 1 mJy has been obtained.

An extensive follow-up programme is begin undertaken in the ELAIS regions, utilizing a vast battery of telescopes around the world and also a number of satellites. Radio observations at 20 cm using the VLA and ATCA radio telescopes have been obtained. The aim of these observations were to study the well know radio-infrared correlation established for the IRAS sources to radio and infrared fluxes never reached before. The radio catalogues obtained from these observation have been published in two papers on the MNRAS. Moreover in collaboration with F. La Franca (University of Rome) and S. Oliver (Imperial College, London) the optical spectroscopic follow-up data obtained with the multi-fibres 2dF (Australian Telescope) in the south region called S2 were analyzed. In the same contest of follow-up observation of ELAIS sources, single slit spectroscopic data of faint ISO-CAM sources (Flux0.4 mJy) were obtained using the 3.6m ESO Telescope at La Silla (Chile).

The results of these observation have shown that at brighter ISOCAM fluxes the 15m band is highly efficient in detecting AGN, especially type 1 at z > 1-1.5. At fainter ISOCAM fluxes the starburst population (including a significant fraction of dust obscured starbursts) is highly dominant, although the redshift distribution for these galaxies shows a peak at much lower z than previously found at similar flux levels in the CFRS ISOCAM survey.