2006A&A...451..881B

The ESO-Spitzer extragalactic Imaging Survey (ESIS) is the optical follow up of the Spitzer Wide-Area InfraRed Extragalactic (SWIRE) survey in the ELAIS-S1 area. The multiwavelength study of galaxy emission is the key to understand the interplay of the various components of galaxies and to trace their role in cosmic evolution. ESIS provides optical identification and colors of Spitzer IR galaxies and builds the bases for photometric redshift estimates. This paper presents B, V, R Wide Field Imager observations of the first 1.5 square degree of the ESIS survey. Data reduction is described including astrometric calibration, illumination and color corrections. Synthetic sources are simulated in scientific and super-sky-flat images, with the purpose of estimating completeness and photometric accuracy for the survey. Number counts and color distributions are compared to literature observational and theoretical data, including non-evolutionary, PLE, evolutionary and semi-analytic ΛCDM galaxy models, as well as Milky Way stellar predictions. The ELAIS-S1 area benefits from extensive follow-up from X-ray to radio frequencies: some potential uses of the multi-wavelength observations are illustrated. Object coordinates are defined with an accuracy as good as ∼0.15[arcsec] rms with respect to GSC 2.2; flux uncertainties are ∼2, 10, 20% at mag. 20, 23, 24 respectively (Vega); we reach 95% completeness at B, V∼25 and R∼24.5. ESIS galaxy number counts are in good agreement with previous works and are best reproduced by evolutionary and hierarchical ΛCDM scenarios. Optical-Spitzer color-color plots promise to be very powerful tools to disentangle different classes of sources (e.g. AGNs, starbursts, quiescent galaxies). Ultraviolet GALEX data are matched to optical and Spitzer samples, leading to a discussion of galaxy properties in the UV-to-24µm color space. The spectral energy distribution of a few objects, from the X-rays to the far-IR are presented as examples of the multi-wavelength study of galaxy emission components in different spectral domains.