zCOSMOS (P.I. Simon Lilly) is a large redshift survey that is being undertaken in the COSMOS field using the VIMOS spectrograph mounted at the Melipal Unit Telescope of the VLT at ESO's Cerro Paranal Observatory, Chile. zCOSMOS (ESO Large Programme LP175.A-0839) has been awarded about 600 hours of Service Mode observing time on the ESO VLT, making it the largest single observing project undertaken so far on that facility.

The zCOSMOS redshift survey has been designed to efficiently utilize VIMOS by splitting the survey into two parts. The first, zCOSMOS-bright, aims to produce a redshift survey of approximately 20,000 I-band selected galaxies at redshifts z < 1.2. Covering the approximately 1.7 deg2 of the COSMOS field (essentially the full ACS-covered area), the transverse dimension at z ~ 1 is 75 Mpc. The second part, zCOSMOS-deep, will observe about 10,000 galaxies selected through well-defined colour selection criteria which mostly lie at 1.5 < z < 3.0. Simply to keep the required amount of telescope time manageable, the field of zCOSMOS-deep is restricted to the central 1 deg2 of the COSMOS field.

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