Accurate photometric redshifts for the CFHT legacy survey calibrated using the VIMOS VLT deep survey

O. Ilbert; S. Arnouts; H. J. McCracken; M. Bolzonella; E. Bertin; O. Le Fèvre; Y. Mellier; G. Zamorani; R. Pellò; A. Iovino; L. Tresse; V. Le Brun; D. Bottini; B. Garilli; D. Maccagni; J. P. Picat; R. Scaramella; M. Scodeggio; G. Vettolani; A. Zanichelli; C. Adami; S. Bardelli; A. Cappi; S. Charlot; P. Ciliegi; T. Contini; O. Cucciati; S. Foucaud; P. Franzetti; I. Gavignaud; L. Guzzo; B. Marano; C. Marinoni; A. Mazure; B. Meneux; R. Merighi; S. Paltani; A. Pollo; L. Pozzetti; M. Radovich; E. Zucca; M. Bondi; A. Bongiorno; G. Busarello; S. De La Torre; L. Gregorini; F. Lamareille; G. Mathez; P. Merluzzi; V. Ripepi; D. Rizzo; D. Vergani

doi:10.1051/0004-6361:20065138

Accurate photometric redshifts for the CFHT legacy survey calibrated using the VIMOS VLT deep survey

O. Ilbert, S. Arnouts, H. J. McCracken, M. Bolzonella, E. Bertin, O. Le Fèvre, Y. Mellier, G. Zamorani, R. Pellò, A. Iovino, L. Tresse, V. Le Brun, D. Bottini, B. Garilli, D. Maccagni, J. P. Picat, R. Scaramella, M. Scodeggio, G. Vettolani, A. ZanichelliC. Adami, S. Bardelli, A. Cappi, S. Charlot, P. Ciliegi, T. Contini, O. Cucciati, S. Foucaud, P. Franzetti, I. Gavignaud, L. Guzzo, B. Marano, C. Marinoni, A. Mazure, B. Meneux, R. Merighi, S. Paltani, A. Pollo, L. Pozzetti, M. Radovich, E. Zucca, M. Bondi, A. Bongiorno, G. Busarello, S. De La Torre, L. Gregorini, F. Lamareille, G. Mathez, P. Merluzzi, V. Ripepi, D. Rizzo, D. Vergani

Exact Sciences School

Research output: Contribution to journal › Review article › peer-review

1296 Citations (Scopus)

Abstract

Aims. We present and release photometric redshifts for a uniquely large and deep sample of 522286 objects with i′_AB ≤25 in the Canada-France Hawaii Telescope Legacy Survey (CFHTLS) "Deep Survey" fields D1, D2, D3, and D4, which cover a total effective area of 3.2 deg ². Methods. We use 3241 spectroscopic redshifts with 0 ≤ z ≤ 5 from the VIMOS VLT Deep Survey (VVDS) as a calibration and training set to derive these photometric redshifts. Using the "Le Phare" photometric redshift code, we developed a robust calibration method based on an iterative zero-point refinement combined with a template optimisation procedure and the application of a Bayesian approach. This method removes systematic trends in the photometric redshifts and significantly reduces the fraction of catastrophic errors (by a factor of 2), a significant improvement over traditional methods. We use our unique spectroscopic sample to present a detailed assessment of the robustness of the photometric redshift sample. Results. For a sample selected at i′_AB ≤24, we reach a redshift accuracy of σ_Δz/(1+z)= 0.029 with η = 3.8% of catastrophic errors (η is defined strictly as those objects with |Δz|/(1 + z) > 0.15). The reliability of our photometric redshifts decreases for faint objects: we find σ_Δz/(1+z) = 0.025,0.034 and η = 1.9%, 5.5% for samples selected at i′_AB = 17.5-22.5 and 22.5-24 respectively. We find that the photometric redshifts of starburst galaxies are less reliable: although these galaxies represent only 22% of the spectroscopic sample, they are responsible for 50% of the catastrophic errors. An analysis as a function of redshift demonstrates that our photometric redshifts work best in the redshift range 0.2 ≤; z ≤ 1.5. We find an excellent agreement between the photometric and the VVDS spectroscopic redshift distributions at i′_AB ≤ 24. Finally, we compare the redshift distributions of i′ selected galaxies on the four CFHTLS deep fields, showing that cosmic variance is still present on fields of 0.7-0.9 deg². These photometric redshifts are made publicly available at http://terapix.iap.fr (complete ascii catalogues) and http://cencos.oamp.fr/cencos/CFHTLS/ (searchable database interface).

Original language	English
Pages (from-to)	841-856
Number of pages	16
Journal	Astronomy and Astrophysics
Volume	457
Issue number	3
DOIs	https://doi.org/10.1051/0004-6361:20065138
Publication status	Published - Oct 2006

Keywords

Galaxies: distances and redshifts
Galaxies: photometry
Methods: data analysis

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

Access to Document

10.1051/0004-6361:20065138

Cite this

Ilbert, O., Arnouts, S., McCracken, H. J., Bolzonella, M., Bertin, E., Le Fèvre, O., Mellier, Y., Zamorani, G., Pellò, R., Iovino, A., Tresse, L., Le Brun, V., Bottini, D., Garilli, B., Maccagni, D., Picat, J. P., Scaramella, R., Scodeggio, M., Vettolani, G., ... Vergani, D. (2006). Accurate photometric redshifts for the CFHT legacy survey calibrated using the VIMOS VLT deep survey. Astronomy and Astrophysics, 457(3), 841-856. https://doi.org/10.1051/0004-6361:20065138

@article{ba9a9af8e6a14a758393b2221e22f755,

title = "Accurate photometric redshifts for the CFHT legacy survey calibrated using the VIMOS VLT deep survey",

abstract = "Aims. We present and release photometric redshifts for a uniquely large and deep sample of 522286 objects with i′AB ≤25 in the Canada-France Hawaii Telescope Legacy Survey (CFHTLS) {"}Deep Survey{"} fields D1, D2, D3, and D4, which cover a total effective area of 3.2 deg 2. Methods. We use 3241 spectroscopic redshifts with 0 ≤ z ≤ 5 from the VIMOS VLT Deep Survey (VVDS) as a calibration and training set to derive these photometric redshifts. Using the {"}Le Phare{"} photometric redshift code, we developed a robust calibration method based on an iterative zero-point refinement combined with a template optimisation procedure and the application of a Bayesian approach. This method removes systematic trends in the photometric redshifts and significantly reduces the fraction of catastrophic errors (by a factor of 2), a significant improvement over traditional methods. We use our unique spectroscopic sample to present a detailed assessment of the robustness of the photometric redshift sample. Results. For a sample selected at i′AB ≤24, we reach a redshift accuracy of σΔz/(1+z)= 0.029 with η = 3.8% of catastrophic errors (η is defined strictly as those objects with |Δz|/(1 + z) > 0.15). The reliability of our photometric redshifts decreases for faint objects: we find σΔz/(1+z) = 0.025,0.034 and η = 1.9%, 5.5% for samples selected at i′AB = 17.5-22.5 and 22.5-24 respectively. We find that the photometric redshifts of starburst galaxies are less reliable: although these galaxies represent only 22% of the spectroscopic sample, they are responsible for 50% of the catastrophic errors. An analysis as a function of redshift demonstrates that our photometric redshifts work best in the redshift range 0.2 ≤; z ≤ 1.5. We find an excellent agreement between the photometric and the VVDS spectroscopic redshift distributions at i′AB ≤ 24. Finally, we compare the redshift distributions of i′ selected galaxies on the four CFHTLS deep fields, showing that cosmic variance is still present on fields of 0.7-0.9 deg2. These photometric redshifts are made publicly available at http://terapix.iap.fr (complete ascii catalogues) and http://cencos.oamp.fr/cencos/CFHTLS/ (searchable database interface).",

keywords = "Galaxies: distances and redshifts, Galaxies: photometry, Methods: data analysis",

author = "O. Ilbert and S. Arnouts and McCracken, {H. J.} and M. Bolzonella and E. Bertin and {Le F{\`e}vre}, O. and Y. Mellier and G. Zamorani and R. Pell{\`o} and A. Iovino and L. Tresse and {Le Brun}, V. and D. Bottini and B. Garilli and D. Maccagni and Picat, {J. P.} and R. Scaramella and M. Scodeggio and G. Vettolani and A. Zanichelli and C. Adami and S. Bardelli and A. Cappi and S. Charlot and P. Ciliegi and T. Contini and O. Cucciati and S. Foucaud and P. Franzetti and I. Gavignaud and L. Guzzo and B. Marano and C. Marinoni and A. Mazure and B. Meneux and R. Merighi and S. Paltani and A. Pollo and L. Pozzetti and M. Radovich and E. Zucca and M. Bondi and A. Bongiorno and G. Busarello and {De La Torre}, S. and L. Gregorini and F. Lamareille and G. Mathez and P. Merluzzi and V. Ripepi and D. Rizzo and D. Vergani",

year = "2006",

month = oct,

doi = "10.1051/0004-6361:20065138",

language = "English",

volume = "457",

pages = "841--856",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

number = "3",

}

Ilbert, O, Arnouts, S, McCracken, HJ, Bolzonella, M, Bertin, E, Le Fèvre, O, Mellier, Y, Zamorani, G, Pellò, R, Iovino, A, Tresse, L, Le Brun, V, Bottini, D, Garilli, B, Maccagni, D, Picat, JP, Scaramella, R, Scodeggio, M, Vettolani, G, Zanichelli, A, Adami, C, Bardelli, S, Cappi, A, Charlot, S, Ciliegi, P, Contini, T, Cucciati, O, Foucaud, S, Franzetti, P, Gavignaud, I, Guzzo, L, Marano, B, Marinoni, C, Mazure, A, Meneux, B, Merighi, R, Paltani, S, Pollo, A, Pozzetti, L, Radovich, M, Zucca, E, Bondi, M, Bongiorno, A, Busarello, G, De La Torre, S, Gregorini, L, Lamareille, F, Mathez, G, Merluzzi, P, Ripepi, V, Rizzo, D & Vergani, D 2006, 'Accurate photometric redshifts for the CFHT legacy survey calibrated using the VIMOS VLT deep survey', Astronomy and Astrophysics, vol. 457, no. 3, pp. 841-856. https://doi.org/10.1051/0004-6361:20065138

TY - JOUR

T1 - Accurate photometric redshifts for the CFHT legacy survey calibrated using the VIMOS VLT deep survey

AU - Ilbert, O.

AU - Arnouts, S.

AU - McCracken, H. J.

AU - Bolzonella, M.

AU - Bertin, E.

AU - Le Fèvre, O.

AU - Mellier, Y.

AU - Zamorani, G.

AU - Pellò, R.

AU - Iovino, A.

AU - Tresse, L.

AU - Le Brun, V.

AU - Bottini, D.

AU - Garilli, B.

AU - Maccagni, D.

AU - Picat, J. P.

AU - Scaramella, R.

AU - Scodeggio, M.

AU - Vettolani, G.

AU - Zanichelli, A.

AU - Adami, C.

AU - Bardelli, S.

AU - Cappi, A.

AU - Charlot, S.

AU - Ciliegi, P.

AU - Contini, T.

AU - Cucciati, O.

AU - Foucaud, S.

AU - Franzetti, P.

AU - Gavignaud, I.

AU - Guzzo, L.

AU - Marano, B.

AU - Marinoni, C.

AU - Mazure, A.

AU - Meneux, B.

AU - Merighi, R.

AU - Paltani, S.

AU - Pollo, A.

AU - Pozzetti, L.

AU - Radovich, M.

AU - Zucca, E.

AU - Bondi, M.

AU - Bongiorno, A.

AU - Busarello, G.

AU - De La Torre, S.

AU - Gregorini, L.

AU - Lamareille, F.

AU - Mathez, G.

AU - Merluzzi, P.

AU - Ripepi, V.

AU - Rizzo, D.

AU - Vergani, D.

PY - 2006/10

Y1 - 2006/10

N2 - Aims. We present and release photometric redshifts for a uniquely large and deep sample of 522286 objects with i′AB ≤25 in the Canada-France Hawaii Telescope Legacy Survey (CFHTLS) "Deep Survey" fields D1, D2, D3, and D4, which cover a total effective area of 3.2 deg 2. Methods. We use 3241 spectroscopic redshifts with 0 ≤ z ≤ 5 from the VIMOS VLT Deep Survey (VVDS) as a calibration and training set to derive these photometric redshifts. Using the "Le Phare" photometric redshift code, we developed a robust calibration method based on an iterative zero-point refinement combined with a template optimisation procedure and the application of a Bayesian approach. This method removes systematic trends in the photometric redshifts and significantly reduces the fraction of catastrophic errors (by a factor of 2), a significant improvement over traditional methods. We use our unique spectroscopic sample to present a detailed assessment of the robustness of the photometric redshift sample. Results. For a sample selected at i′AB ≤24, we reach a redshift accuracy of σΔz/(1+z)= 0.029 with η = 3.8% of catastrophic errors (η is defined strictly as those objects with |Δz|/(1 + z) > 0.15). The reliability of our photometric redshifts decreases for faint objects: we find σΔz/(1+z) = 0.025,0.034 and η = 1.9%, 5.5% for samples selected at i′AB = 17.5-22.5 and 22.5-24 respectively. We find that the photometric redshifts of starburst galaxies are less reliable: although these galaxies represent only 22% of the spectroscopic sample, they are responsible for 50% of the catastrophic errors. An analysis as a function of redshift demonstrates that our photometric redshifts work best in the redshift range 0.2 ≤; z ≤ 1.5. We find an excellent agreement between the photometric and the VVDS spectroscopic redshift distributions at i′AB ≤ 24. Finally, we compare the redshift distributions of i′ selected galaxies on the four CFHTLS deep fields, showing that cosmic variance is still present on fields of 0.7-0.9 deg2. These photometric redshifts are made publicly available at http://terapix.iap.fr (complete ascii catalogues) and http://cencos.oamp.fr/cencos/CFHTLS/ (searchable database interface).

AB - Aims. We present and release photometric redshifts for a uniquely large and deep sample of 522286 objects with i′AB ≤25 in the Canada-France Hawaii Telescope Legacy Survey (CFHTLS) "Deep Survey" fields D1, D2, D3, and D4, which cover a total effective area of 3.2 deg 2. Methods. We use 3241 spectroscopic redshifts with 0 ≤ z ≤ 5 from the VIMOS VLT Deep Survey (VVDS) as a calibration and training set to derive these photometric redshifts. Using the "Le Phare" photometric redshift code, we developed a robust calibration method based on an iterative zero-point refinement combined with a template optimisation procedure and the application of a Bayesian approach. This method removes systematic trends in the photometric redshifts and significantly reduces the fraction of catastrophic errors (by a factor of 2), a significant improvement over traditional methods. We use our unique spectroscopic sample to present a detailed assessment of the robustness of the photometric redshift sample. Results. For a sample selected at i′AB ≤24, we reach a redshift accuracy of σΔz/(1+z)= 0.029 with η = 3.8% of catastrophic errors (η is defined strictly as those objects with |Δz|/(1 + z) > 0.15). The reliability of our photometric redshifts decreases for faint objects: we find σΔz/(1+z) = 0.025,0.034 and η = 1.9%, 5.5% for samples selected at i′AB = 17.5-22.5 and 22.5-24 respectively. We find that the photometric redshifts of starburst galaxies are less reliable: although these galaxies represent only 22% of the spectroscopic sample, they are responsible for 50% of the catastrophic errors. An analysis as a function of redshift demonstrates that our photometric redshifts work best in the redshift range 0.2 ≤; z ≤ 1.5. We find an excellent agreement between the photometric and the VVDS spectroscopic redshift distributions at i′AB ≤ 24. Finally, we compare the redshift distributions of i′ selected galaxies on the four CFHTLS deep fields, showing that cosmic variance is still present on fields of 0.7-0.9 deg2. These photometric redshifts are made publicly available at http://terapix.iap.fr (complete ascii catalogues) and http://cencos.oamp.fr/cencos/CFHTLS/ (searchable database interface).

KW - Galaxies: distances and redshifts

KW - Galaxies: photometry

KW - Methods: data analysis

UR - http://www.scopus.com/inward/record.url?scp=33750022004&partnerID=8YFLogxK

U2 - 10.1051/0004-6361:20065138

DO - 10.1051/0004-6361:20065138

M3 - Review article

AN - SCOPUS:33750022004

SN - 0004-6361

VL - 457

SP - 841

EP - 856

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

IS - 3

ER -

Accurate photometric redshifts for the CFHT legacy survey calibrated using the VIMOS VLT deep survey

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