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 Fevre, S. Lilly, D. Looper, C. Maier, V. Mainieri, Y. Mellier, M. Mignoli, T. Murayama, R. Pello, Y. Peng, E. Perez-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

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

931 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 chi(2) 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 ([O II], H beta, H alpha, and Ly alpha) 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., Delta z = z(s) - z(p)) indicates a dispersion of sigma(Delta z)/((1+zs)) = 0.007 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 sigma(Delta z/(1+zs)) = 0.012. The deep NIR and Infrared Array Camera coverage enables the photo-z to be extended to z similar to 2, albeit with a lower accuracy (sigma(Delta z/(1+zs)) = 0.06 at i(AB)(+) similar to 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 zm = 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
JournalThe Astrophysical Journal
Issue number2
Publication statusPublished - 10-Jan-2009
Externally publishedYes


  • galaxies: distances and redshifts
  • galaxies: evolution
  • galaxies: formation
  • TO 2.5
  • DUST
  • 1ST

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