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