The PAU survey: photometric redshift estimation in deep wide fields

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 deg², for ~1.8 million objects up to iAB< 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 (zb), obtained through the combination of the bcnz and the BB-only photo-z. Comparing with spectroscopic redshift estimates (zₛ), we obtain a σ ₆₈ 0.020 for all galaxies with iAB< 23 and a typical bias |zb\!-\!zₛ| smaller than 0.01. For zb ~ (0.10\!-\!0.75), we find σ 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 zb. 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.