zCOSMOS: A Large VLT/VIMOS Redshift Survey Covering 0 &lt;<i>z</i>&lt; 3 in the COSMOS Field

Abstract

zCOSMOS is a large-redshift survey that is being undertaken in the COSMOS field using 600 hr of observation&#13;\nwith the VIMOS spectrograph on the 8 m VLT. The survey is designed to characterize the environments of COSMOS&#13;\ngalaxies from the 100 kpc scales of galaxy groups up to the 100 Mpc scale of the cosmic web and to produce diagnostic&#13;\ninformation on galaxies and active galactic nuclei. The zCOSMOS survey consists of two parts: (1) zCOSMOSbright,&#13;\na magnitude-limited I-band I_(AB) &lt; 22.5 sample of about 20,000 galaxies with 0.1 &lt; z &lt; 1.2 covering the whole&#13;\n1.7 deg^2 COSMOS ACS field, for which the survey parameters at z ~ 0.7 are designed to be directly comparable to&#13;\nthose of the 2dFGRS at z ~ 0.1; and (2) zCOSMOS-deep, a survey of approximately 10,000 galaxies selected through&#13;\ncolor-selection criteria to have 1.4 &lt; z &lt; 3.0, within the central 1 deg^2. This paper describes the survey design and the&#13;\nconstruction of the target catalogs and briefly outlines the observational program and the data pipeline. In the first&#13;\nobserving season, spectra of 1303 zCOSMOS-bright targets and 977 zCOSMOS-deep targets have been obtained.&#13;\nThese are briefly analyzed to demonstrate the characteristics that may be expected from zCOSMOS, and particularly&#13;\nzCOSMOS-bright, when it is finally completed between 2008 and 2009. The power of combining spectroscopic and&#13;\nphotometric redshifts is demonstrated, especially in correctly identifying the emission line in single-line spectra and in&#13;\ndetermining which of the less reliable spectroscopic redshifts are correct and which are incorrect. These techniques&#13;\nbring the overall success rate in the zCOSMOS-bright so far to almost 90% and to above 97% in the 0.5 &lt; z &lt; 0.8&#13;\nredshift range. Our zCOSMOS-deep spectra demonstrate the power of our selection techniques to isolate high-redshift&#13;\ngalaxies at 1.4 &lt; z &lt; 3.0 and of VIMOS to measure their redshifts using ultraviolet absorption lines.