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 $\sim$50 deg${}^2$, for $\sim$1.8 million objects up to $i_{\text{AB}}<23$. 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 ($z_{\text{b}}$), obtained through the combination of the BCNZ and the BB-only photo-$z$. Comparing with spectroscopic redshifts estimates ($z_{\text{s}}$), we obtain a ${\sigma }_{68}\simeq 0.019$ for all galaxies with $i_{\text{AB}}<23$ and a typical bias $|z_{\text{b}}-z_{\text{s}}|$ smaller than 0.01. For $z_{\text{b}}\sim (0.10-0.75)$ we find ${\sigma }_{68}\simeq (0.003-0.02)$, 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 $z_{\text{b}}$. These photo-$z$ catalogues will facilitate important science cases, such as the study of galaxy clustering and intrinsic alignment at high redshifts ($z\lesssim 1$) and faint magnitudes.

24 pages, 26 figures, submitted to MNRAS

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• TOPz: Photometric redshifts using template fitting applied to the GAMA survey