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The PAU Survey: an improved photo-z sample in the COSMOS field

Alarcon, Alex; Gaztanaga, Enrique; Eriksen, Martin; Baugh, Carlton M; Cabayol, Laura; Casas, Ricard; Carretero, Jorge; Castander, Francisco J; De Vicente, Juan; Fernandez, Enrique; Garcia-Bellido, Juan; Hildebrandt, Hendrik; Hoekstra, Henk; Joachimi, Benjamin; Manzoni, Giorgio; Miquel, Ramon; Norberg, Peder; Padilla, Cristobal; Renard, Pablo; Sanchez, Eusebio; Serrano, Santiago; Sevilla-Noarbe, Ignacio; Siudek, Malgorzata; Tallada-Crespí, Pau

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Alex Alarcon

Enrique Gaztanaga

Martin Eriksen

Laura Cabayol

Ricard Casas

Jorge Carretero

Francisco J Castander

Juan De Vicente

Enrique Fernandez

Juan Garcia-Bellido

Hendrik Hildebrandt

Henk Hoekstra

Benjamin Joachimi

Giorgio Manzoni

Ramon Miquel

Cristobal Padilla

Pablo Renard

Eusebio Sanchez

Santiago Serrano

Ignacio Sevilla-Noarbe

Malgorzata Siudek

Pau Tallada-Crespí


We present – and make publicly available – accurate and precise photometric redshifts in the ACS footprint from the COSMOS field for objects with iAB ≤ 23. The redshifts are computed using a combination of narrow-band photometry from PAUS, a survey with 40 narrow bands spaced at 100A˚ intervals covering the range from 4500 to 8500A˚⁠, and 26 broad, intermediate, and narrow bands covering the UV, visible and near-infrared spectrum from the COSMOS2015 catalogue. We introduce a new method that models the spectral energy distributions as a linear combination of continuum and emission-line templates and computes its Bayes evidence, integrating over the linear combinations. The correlation between the UV luminosity and the O II line is measured using the 66 available bands with the zCOSMOS spectroscopic sample, and used as a prior which constrains the relative flux between continuum and emission-line templates. The flux ratios between the O II line and Hα, Hβ and OIII are similarly measured and used to generate the emission-line templates. Comparing to public spectroscopic surveys via the quantity Δz ≡ (zphoto − zspec)/(1 + zspec), we find the photometric redshifts to be more precise than previous estimates, with σ68(Δz) ≈ (0.003, 0.009) for galaxies at magnitude iAB ∼ 18 and iAB ∼ 23, respectively, which is three times and 1.66 times tighter than COSMOS2015. Additionally, we find the redshifts to be very accurate on average, yielding a median of the Δz distribution compatible with |median(Δz)| ≤ 0.001 at all redshifts and magnitudes considered. Both the added PAUS data and new methodology contribute significantly to the improved results. The catalogue produced with the technique presented here is expected to provide a robust redshift calibration for current and future lensing surveys, and allows one to probe galaxy formation physics in an unexplored luminosity-redshift regime, thanks to its combination of depth, completeness, and excellent redshift precision and accuracy.


Alarcon, A., Gaztanaga, E., Eriksen, M., Baugh, C. M., Cabayol, L., Casas, R., …Tallada-Crespí, P. (2021). The PAU Survey: an improved photo-z sample in the COSMOS field. Monthly Notices of the Royal Astronomical Society, 501(4), 6103-6122.

Journal Article Type Article
Acceptance Date Nov 17, 2020
Online Publication Date Jan 22, 2021
Publication Date 2021-03
Deposit Date Jul 1, 2021
Publicly Available Date Jul 1, 2021
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 501
Issue 4
Pages 6103-6122


Published Journal Article (2.9 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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