The zCosmos 10k-bright spectroscopic sample

Simon J. Lilly, Vincent Le Brun, Christian Maier, Vincenzo Mainieri, Marco Mignoli, Marco Scodeggio, Gianni Zamorani, Marcella Carollo, Thierry Contini, Jean Paul Kneib, Olivier Le Fèvre, Alvio Renzini, Sandro Bardelli, Micol Bolzonella, Angela Bongiorno, Karina Caputi, Graziano Coppa, Olga Cucciati, Sylvain De La Torre, Loic De RavelPaolo Franzetti, Bianca Garilli, Angela Iovino, Pawel Kampczyk, Katarina Kovac, Christian Knobel, Fabrice Lamareille, Jean Francois Le Borgne, Roser Pello, Yingjie Peng, Enrique Pérez-Montero, Elena Ricciardelli, John D. Silverman, Masayuki Tanaka, Lidia Tasca, Laurence Tresse, Daniela Vergani, Elena Zucca, Olivier Ilbert, Mara Salvato, Pascal Oesch, Umi Abbas, Dario Bottini, Peter Capak, Alberto Cappi, Paolo Cassata, Andrea Cimatti, Martin Elvis, Marco Fumana, Luigi Guzzo, Gunther Hasinger, Anton Koekemoer, Alexei Leauthaud, Dario MacCagni, Christian Marinoni, Henry McCracken, Pierdomenico Memeo, Baptiste Meneux, Cristiano Porciani, Lucia Pozzetti, David Sanders, Roberto Scaramella, Claudia Scarlata, Nick Scoville, Patrick Shopbell, Yoshiaki Taniguchi

Research output: Contribution to journalArticlepeer-review

491 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)218-229
Number of pages12
JournalAstrophysical Journal, Supplement Series
Issue number2
StatePublished - 2009


  • Cosmology: observations
  • Galaxies: active
  • Galaxies: distances and redshifts
  • Galaxies: evolution
  • Large-scale structure of universe
  • Quasars: general
  • Surveys


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