The PAU survey: photometric redshift estimation in deep wide fields

ABSTRACT We present photometric redshifts (photo-z) for the deep wide fields of the Physics of the Accelerating Universe Survey (PAUS), covering an area of 50 deg^2, for 1. 8 million objects up to i ₀₁ 23. The PAUS deep wide fields overlap with the W1 and W3 fields from CFHTLenS and the G09 field from KiDS/GAMA. Photo-z are estimated using the 40 narrow bands (NB) of PAUS and the broad-bands (BB) of CFHTLenS and KiDS. We compute the redshifts with the SED template-fitting code bcnz, with a modification in the calibration technique of the zero-point between the observed and the modelled fluxes, that removes any dependence on spectroscopic redshift samples. We enhance the redshift accuracy by introducing an additional photo-z estimate (z ₁), obtained through the combination of the bcnz and the BB-only photo-z. Comparing with spectroscopic redshift estimates (z ₒ), we obtain a ₆₈ 0. 020 for all galaxies with i ₀₁ 23 and a typical bias |z ₁\!-\!z ₒ| smaller than 0. 01. For z ₁ (0. 10\!-\!0. 75), we find ₆₈ (0. 003\!-\!0. 02), this is a factor of 10\!-\!2 higher accuracy than the corresponding BB-only results. We obtain similar performance when we split the samples into red (passive) and blue (active) galaxies. We validate the redshift probability p (z) obtained by bcnz and compare its performance with that of z ₁. These photo-z catalogues will facilitate important science cases, such as the study of galaxy clustering and intrinsic alignment at high redshifts (z 1) and faint magnitudes.