5. ELAIS : The European Large Area ISO Survey

The Universe is a physical object. Physical objects have shapes and sizes.
So, a major goal of observational cosmology is to measure the shape and size
of the Universe (within appropriate mathematical theory relating to
geometry), or else to convincingly show that these are unmeasurable.
The alternative, to suppose that the Universe is a spiritual object,
without a shape or size, is not part of the domain of science.


Boudewijn F. Roukema,
"Observational Constraints on the Topology
(Global Geometry) of the Universe", 2000
astro-ph/0201092

The largest project carried out in ISO Open Time and the largest ISO non-serendipitous survey, the European Large Area ISO Survey (ELAIS, Rowan-Robinson, 2004; Oliver, 2000) provides a link between IRAS all-sky survey and ISO deeper surveys, covering around 12  $\square^\circ$ of the sky at 15 $\mu$m and 90 $\mu$m, nearly 6  $\square^\circ$ at 6.7 $\mu$m together with 1  $\square^\circ$ at 175 $\mu$m. The survey used ISOCAM at the two shorter wavelengths and ISOPHOT at the two longer ones, obtaining a total of 375 hours of scientifically validated data. Since the project approval, the ELAIS consortium, led by Imperial College and grown in time to a total of 76 collaborators from 30 European institutes, has undertaken an extensive program of ground-based optical and near-infrared imaging and spectroscopy. Thanks to such an extensive multi-wavelength coverage, the ELAIS fields have now arguably become the best studied sky areas of their size, and natural targets of on-going or planned large-area surveys with the most powerful ground- and space-based facilities. This Chapter outlines the broad scientific objectives of this project and describes the selection of the observing modes and survey fields. It also details the execution of the ISO observations and the multi-wavelength coverage of the fields.