The VIMOS integral field unit:: Data reduction methods and quality assessment

With the new generation of spectrographs, integral field spectroscopy is becoming a widely used observational technique. The Integral Field Unit (IFU) of the Visible Multi - Object Spectrograph (VIMOS) on the ESO VLT allows sampling of a field as large as 54 '' x 54 '', covered by 6400 fibers coupled with microlenses. We present here the methods of the data-processing software that has been developed to extract the astrophysical signal of faint sources from the VIMOS IFU observations. We focus on the treatment of the fiber-to-fiber relative transmission and the sky subtraction, and the dedicated tasks we have built to address the peculiarities and unprecedented complexity of the data set. We review the automated process we have developed under the VIPGI data organization and reduction environment (Scodeggio et al. 2005), along with the quality control performed to validate the process. The VIPGI IFU data-processing environment has been available to the scientific community to process VIMOS IFU data since 2003 November.