a 100 deg2 PAUS will provide 3 million redshifts to iAB>22.5 (30 times more than currently available)
a 100 deg2 PAUS with 45 color bands is equivalent to 4500 deg2 single band imaging survey
A number of large surveys (e.g. KiDS, DES, SDSS, DESI) aim to map the 3D structure of the Universe to understand the nature of dark matter and dark energy. To achieve the required statistical precision, these focus on large scales, sparse samples of selected spectroscopic targets, or restrict the line-of-sight resolution by employing photometric redshifts based on a few broad- bands (BB). In contrast, studies aiming to explore the role of environment are limited to the small scales provided by pencil-beam surveys. We need to bridge this gap and probe the intermediate to small scales (below 10-20 Mpc/h), i.e. the weakly non-linear regime where the statistical signal-to-noise is largest. Our currently limited understanding of these scales, where baryonic and environmental effects become rel- evant, has to improve dramatically over the coming years to allow for a robust separation of cosmological and galaxy formation effects. This requires surveying large contiguous areas while simultaneously achieving a high number density of galaxies with sub-percent photo- metric redshift accuracy. This is now possible thanks to PAUCam: a unique combination of a large field-of-view and 40 narrow-band (NB) filters (12.5nm FWHM) that span the wavelength range from 450nm to 850nm and that was commissioned successfully in June 2015 on the WHT. This exquisite wavelength sampling results in photometric redshifts with a precision that approaches that of spectroscopic measurements, while being able to cover large areas of sky.