EFOSC2 Spectroscopy of SWIRE-CDFS galaxies

ABSTRACT We present the optical spectra of a sample of 34 SWIRE-CDFS sources observed withEFOSC2 on the ESO 3.6m Telescope. We have used the spectra and spectroscopicredshifts to validate our photometric redshift codes and SED template fitting meth-ods. 12 of our sources are Infrared Luminous Galaxies. Of these, five belong to theclass of ULIRGs and one to the class of HLIRGs with evidence of both an AGN andstarburst component contributing to their extreme infrared luminosity for 3, starburstcontributing for 1 and AGN contributing for 2 of them.Key words: 1 INTRODUCTIONIn recent years, extragalactic surveys have revolutionizedour view of the high-redshift Universe, showing that theredshift range 0.5 < z < 3.0 witnessed an extraordinarytransformation in the demographics of starburst and AGNactivity in galaxies. The factors that drove these changesare however unclear. Consequently, the properties of largesamples of sources are the current driving force behind mod-ern extragalactic surveys (e.g. Lonsdale et al. 2003; Eales etal. 2010; Oliver et al. 2010). However, either most of thesources in these surveys are too faint for spectroscopic ob-servations or it is not cost and time effective to acquirelarge spectroscopic redshift samples using the current fa-cilities. Photometric techniques provide an excellent tool forestimating redshifts, essential for statistical studies of thegalaxies’ properties and evolution with only a fraction ofthe observing time required by spectroscopic surveys. Thesetechniques are faster and can estimate redshifts beyond thespectroscopic limit with the main handicap of possessinglarger errors than spectroscopic techniques. In order to min-imize these statistical errors: i) more bands are needed to beincluded in the photometric computation ii) optical spectro-scopic redshifts have to be used to calibrate and validate thephotometric redshift codes.In this paper we use the EFOSC2 on the 3.6m ESO telescopeto obtain optical spectroscopy of galaxies selected from the