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Published October 2009 | Published
Journal Article Open

The zCOSMOS 10k-Bright Spectroscopic Sample


We present spectroscopic redshifts of a large sample of galaxies with I_(AB) < 22.5 in the COSMOS field, measured from spectra of 10,644 objects that have been obtained in the first two years of observations in the zCOSMOS-bright redshift survey. These include a statistically complete subset of 10,109 objects. The average accuracy of individual redshifts is 110 km s^(–1), independent of redshift. The reliability of individual redshifts is described by a Confidence Class that has been empirically calibrated through repeat spectroscopic observations of over 600 galaxies. There is very good agreement between spectroscopic and photometric redshifts for the most secure Confidence Classes. For the less secure Confidence Classes, there is a good correspondence between the fraction of objects with a consistent photometric redshift and the spectroscopic repeatability, suggesting that the photometric redshifts can be used to indicate which of the less secure spectroscopic redshifts are likely right and which are probably wrong, and to give an indication of the nature of objects for which we failed to determine a redshift. Using this approach, we can construct a spectroscopic sample that is 99% reliable and which is 88% complete in the sample as a whole, and 95% complete in the redshift range 0.5 < z < 0.8. The luminosity and mass completeness levels of the zCOSMOS-bright sample of galaxies is also discussed.

Additional Information

© 2009 The American Astronomical Society. Received 2009 March 19; accepted 2009 August 21; published 2009 September 15. Efficient execution of such a large program in Service Mode on the VLT requires the efforts of many individual observatory staff at ESO, both in Garching and on Cerro Paranal, and we gratefully acknowledge the contribution of these many and regrettably sometimes anonymous individuals to our project. The zCOSMOS program builds on many of the hardware and software tools built by the VIMOS/VVDS team, and we acknowledge here the contribution of those in the VIMOS/ VVDS team who are not part of the zCOSMOS project. Finally, we acknowledge with appreciation the contributions of those many individuals not listed as authors who have worked, directly or indirectly, to produce the superb imaging data on which the COSMOS survey is based.

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Published - Lilly2009p6124Astrophys_J_Suppl_S.pdf


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August 21, 2023
October 19, 2023