The VIRMOS very wide integral field unit for the VLT: integration and performances

We present the integration and performances of the VLT-VIMOS Integral Field spectroscopy Unit. This unit allows to observe a very large 54x54 arcsec 2 field on the side of the VIMOS instrument multi-object field in the range 0.37 - 1μm. This unit contains 6400 sets of micro-lenses - fibers - micro-lenses, producing the equivalent of a 72 arcmin x 0.67 arcsec slit projected on the sky. Two spatial resolutions (0.67 arcsec and 0.33 arcsec) are offered, coupled with the low and high spectral resolution of VIMOS. After reviewing the design philosophy, we are presenting the main steps and challenges encountered during integration. Calibration tests conducted in France and at the Paranal observatory as well as the data reduction software that has been developed for IFU are discussed. The first sky images of this very wide Integral Field Unit have been obtained in the early 2002 commissioning periods at VLT.