VizieR Online Data Catalog: zCOSMOS-bright catalog, DR3 (Lilly+, 2007)

zCOSMOS (P.I. Simon Lilly) is a large redshift survey 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) was awarded about 600 hours of Service Mode observing time on the ESO VLT, which was executed between 2005-2010.

The zCOSMOS redshift survey has been designed to efficiently utilize VIMOS by splitting the survey into two parts. The first, zCOSMOS-bright, which is the subject of DR3, aims to produce a redshift survey of approximately 20000 I-band selected galaxies at redshifts z<1.2. Covering the approximately 1.7deg² of the COSMOS field (essentially the full ACS-covered area), the transverse dimension at z~1 is 75Mpc. The second part, zCOSMOS-deep, observed a smaller number of galaxies selected to mostly lie at higher redshifts, 1.5<z<3.0.

This DR3 release is expected to be the final release of the zCOSMOS-bright spectroscopic catalogue. The full set of extracted 1-dimensional spectra are being released, plus a catalogue in which we give for each target the 1-D spectra filenames, the I-band magnitude used for the selection, as well as the measured redshift and confidence class. A full description of the survey can be found in Lilly et al., 2007ApJS..172...70L, and Lilly et al., 2009ApJS..184..218L, and a future paper to be submitted.

Observations for the DR3 sample were carried out with the VIMOS spectrograph mounted on the 8m VLT/UT3 telescope during extensive Service Mode runs from 2005 to 2009. Observations used the MR grism with 1.0 arcsec slits, yielding a spectral resolution R~600 at 2.5Å/pixel and a spectral range 5550-9450Å. All masks are observed with the slits oriented N-S. The pattern of pointings is such that every target in the central region have had eight opportunities to be selected for observation.

Spectra for 20689 objects could be extracted from the VIMOS observations and are presented in this DR3 release. The targets are selected across the whole 1.7deg² COSMOS field centred at RAJ2000=10:00:2s and DEJ2000=02:13:37 extending over 1.30x1.24deg in the right ascension-declination plane.

The primary input catalogue for slit-mask design was generated using SExtractor (Bertin & Arnouts, 1996A&AS..117..393B) applied to the COSMOS F814W HST/ACS images sampled at 0.03arcsec/pixel (Koekemoer et al., 2007ApJS..172..196K, Leauthaud et al., 2007ApJS..172..219L) in a "hot and cold" two-pass process to first identify bright objects. This substantially reduced the tendency of the HST-based catalogue to "over-resolve" extended galaxies into multiple components. This initial SExtractor catalogue was then "cleaned" by carrying out a detailed comparison with one extracted from a stack of i* images obtained with MEGACAM on the 3.6m Canada-France-Hawaii telescope and processed at the TERAPIX data reduction center in Paris. This catalogue was also used to supplement the ACS catalogue for regions where the ACS images were either unavailable or unusable. The zCOSMOS-bright target catalogue is intended to be simply defined as having an ACS/HST SExtractor "magauto" brightness in the range 15.00<I_AB(814)<22.50.

Generally, objects to be inserted into the slit mask were chosen randomly from the target catalogue. However, a few percent of targets (generally X-ray sources) were designated as "compulsory". These were inserted into the masks with first priority and, as a result, they are about 1.5 times over-represented in the spectroscopic catalogue. Objects strongly suspected of being stars on the basis of morphology and spectral energy distribution were classified as "forbidden" and not included in the mask designs. These comprise about 15% of the I_AB<22.5 sample. The criteria for this exclusion were deliberately quite conservative and as a result about 4% of the spectroscopic targets turn out to be stars.

For each slit there was a primary target. Naturally, sometimes other objects in the target catalogue happened to fall in the same slit. These "secondary targets" were reduced in the same way. If these secondary objects were forbidden, their spectra were anyway reduced and included in the catalogue.

This release DR3 is expected to be the final release of the zCOSMOS-bright dataset. It supersedes, revises and significantly extends the previous releases. The first data release DR1 from October 2007 contained 1264 spectra and a corresponding catalogue. The superseding second data release DR2 from October 2008 contained 10643 spectra and a corresponding catalogue. The ESO Archive Science Group migrated the DR2 release to the Phase 3 infrastructure in February 2014 under Release Number 1. This makes this third DR3 zCOSMOS-bright data release archived under Release Number 2 in the Phase 3 infrastructure.

(2 data files).