Cosmos photometric redshifts with 30-bands for 2-deg2

O. Ilbert, P. Capak, M. Salvato, H. Aussel, H. J. McCracken, D. B. Sanders, N. Scoville, J. Kartaltepe, S. Arnouts, E. Le Floc'H, B. Mobasher, Y. Taniguchi, F. Lamareille, A. Leauthaud, S. Sasaki, D. Thompson, M. Zamojski, G. Zamorani, S. Bardelli, M. BolzonellaA. Bongiorno, M. Brusa, K. I. Caputi, C. M. Carollo, T. Contini, R. Cook, G. Coppa, O. Cucciati, S. De La Torre, L. De Ravel, P. Franzetti, B. Garilli, G. Hasinger, A. Iovino, P. Kampczyk, J. P. Kneib, C. Knobel, K. Kovac, J. F. Le Borgne, V. Le Brun, O. Le Fèvre, S. Lilly, D. Looper, C. Maier, V. Mainieri, Y. Mellier, M. Mignoli, T. Murayama, R. Pellò, Y. Peng, E. Pérez-Montero, A. Renzini, E. Ricciardelli, D. Schiminovich, M. Scodeggio, Y. Shioya, J. Silverman, J. Surace, M. Tanaka, L. Tasca, L. Tresse, D. Vergani, E. Zucca

Research output: Contribution to journalArticlepeer-review

957 Citations (Scopus)


We present accurate photometric redshifts (photo-z) in the 2-deg 2 COSMOS field. The redshifts are computed with 30 broad, intermediate, and narrowbands covering the UV (Galaxy Evolution Explorer), visible near-IR (NIR; Subaru, Canada-France-Hawaii Telescope (CFHT), United Kingdom Infrared Telescope, and National Optical Astronomy Observatory), and mid-IR (Spitzer/IRAC). A χ2 template-fitting method (Le Phare) was used and calibrated with large spectroscopic samples from the Very Large Telescope Visible Multi-Object Spectrograph and the Keck Deep Extragalactic Imaging Multi-Object Spectrograph. We develop and implement a new method which accounts for the contributions from emission lines ([OII], Hβ, Hα, and Lyα) to the spectral energy distributions (SEDs). The treatment of emission lines improves the photo-z accuracy by a factor of 2.5. Comparison of the derived photo-z with 4148 spectroscopic redshifts (i.e., Δz = z s - z p) indicates a dispersion of at i + AB < 22.5, a factor of 2-6 times more accurate than earlier photo-z in the COSMOS, CFHT Legacy Survey, and the Classifying Object by Medium-Band Observations-17 survey fields. At fainter magnitudes i + AB < 24 and z < 1.25, the accuracy is . The deep NIR and Infrared Array Camera coverage enables the photo-z to be extended to z 2, albeit with a lower accuracy ( at i + AB 24). The redshift distribution of large magnitude-selected samples is derived and the median redshift is found to range from z m = 0.66 at 22 < i + AB < 22.5 to z m = 1.06 at 24.5 < i + AB < 25. At i + AB < 26.0, the multiwavelength COSMOS catalog includes approximately 607,617 objects. The COSMOS-30 photo-z enables the full exploitation of this survey for studies of galaxy and large-scale structure evolution at high redshift.

Original languageEnglish
Pages (from-to)1236-1249
Number of pages14
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 2009


  • Galaxies: distances and redshifts
  • Galaxies: evolution
  • Galaxies: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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