The PAU Survey: Early demonstration of photometric redshift performance in the COSMOS field

TL;DR

The PAU Survey demonstrates highly precise photometric redshifts using 40 narrow bands in the COSMOS field, enabling new insights into galaxy evolution and clustering.

Contribution

This work introduces a novel photometric redshift technique with narrow-band data, achieving unprecedented redshift accuracy for wide and deep galaxy surveys.

Findings

Achieves σ₆₈/(1+z) = 0.0037 for i_AB < 22.5

Attains σ₆₈/(1+z) ≈ 0.001 for bright, emission-line galaxies

Demonstrates PAUS's capability to provide precise redshifts for large galaxy samples.

Abstract

The PAU Survey (PAUS) is an innovative photometric survey with 40 narrow bands at the William Herschel Telescope (WHT). The narrow bands are spaced at 100\AA\ intervals covering the range 4500\AA\ to 8500\AA\ and, in combination with standard broad bands, enable excellent redshift precision. This paper describes the technique, galaxy templates and additional photometric calibration used to determine early photometric redshifts from PAUS. Using BCNz2, a new photometric redshift code developed for this purpose, we characterise the photometric redshift performance using PAUS data on the COSMOS field. Comparison to secure spectra from zCOSMOS DR3 shows that PAUS achieves $\sigma_{68} /(1+z) = 0.0037$ to $i_{\mathrm{AB}} < 22.5$ when selecting the best 50% of the sources based on a photometric redshift quality cut. Furthermore, a higher photo-z precision ($\sigma_{68}/(1+z) \sim 0.001$) is obtained for a bright and high quality selection, which is driven by the identification of emission lines. We conclude that PAUS meets its design goals, opening up a hitherto uncharted regime of deep, wide, and dense galaxy survey with precise redshifts that will provide unique insights into the formation, evolution and clustering of galaxies, as well as their intrinsic alignments.