The PAU Survey (PAUS, is an international collaboration between Spain, Holland, Switzerland, Germany, UK to collect a fluxed limited accurate redshift and spectral energy distribution information for millions of galaxies (and stars) to a depth and area never explored before. This is done without the need of target selection which provides a valuable tool to understand sample selection and completeness. To do this, a spanish group had built PAUcam, a large imager (1 degree square FoV, with18 CCD of 4094x2048 pixels each) capable of doing imaging with 40 narrow-band filters (~130A wide in steps of 100A) and 6 wide-band filtres (u,g,r,i,z,Y), which results in high resolution spectra energy distributions for all galaxies in a given field of view. PAUcam was commissioned in the William Herschel 4.2m Telescope (WHT) in the Canary Islands on June 2015. The PAU Survey is using PAUcam to image an area of ?100 deg2 to iAB ~23 to reach a volume of 0.3-0.5 (Gpc/h)3 with a few million redshifts split into 3 to 4 wide fields (of several tens of deg2 each). Deep Broad-Band (BB) photometric measurements have already been obtained by CFHTLenS and KiDS over the same fields and spectroscopic redshifts for calibration are available from the GAMA, VIPERS, DEEP2 and zCOSMOS redshift surveys. This will enable:
  • to improve redshift estimates and target selection incompleteness to reach the accuracy required for large-scale clustering and weak lensing analices in KiDS, DES, DESI, LSST and Euclid
  • detailed studies of intermediate-scale cosmic structure
  • first precise measurement of intrinsic alignments at z ? 0.75
  • cross-correlation techniques for redshift measurements, magnification and sampling variance cancelation studies

A number of large surveys (e.g. KiDS, DES, SDSS, LSST, 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 relevant, 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 redshift accuracy. This is now possible thanks to PAUCam: a unique combination of a large field-of-view and 40 narrow-band 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.
First light image from PAUcam taken in June 2015 at the WHT Telescope. Galaxy M51, known as the Whirlpool galaxy, situated at about 23 million light years from Earth. (Image acquired June 6th, 2015). See
Aim of our participation

PAUCam has been designed and built entirely by a Consortium of Spanish Institutions (in alphabetical order: CIEMAT, Institute of Space Sciences (IEEC-CSIC), IFAE, IFT/UAM, and PIC). The project was funded by the Consolider Ingenio 2010 programme of the Spanish Government. The PAUcam construction and integration was done in Barcelona UAB Campus at IFAE labs with the help of CIEMAT and Institute of Space Sciences' engineers and support from their own lab facilities. This was a join effort and the Institute of Space Sciences is leading the project (F.Castander is the PAUcam Project Scientist). Other main technical contributions from IEEC-CSIC were the procurement and characterization of CCD and filters, as well as other parts, built and operate the optical, cryogenic and electronic test bench, design and build camera guiding and alignment system, design and implement camera optical system and characterization. The Institute of Space Sciences is also leading the PAU Survey Collaboration (E.Gaztanaga is the Survey Director) and the data reduction, community pipeline, automated analysis pipelines and the data distribution in collaboration with PIC (Santi Serrano is the PAUdm Project Manager). Institute of Space Sciences is also leading the scientific exploitation of the PAUS data, including simulations, photometric redshift and clustering forecast and analysis.
CCD test station facility built by ICE and IFAE which consisted of an optical bench delivering mono-chromatic light of a chosen frequency, to a CCD located inside some low-temperature, high vacuum enclosure containing the CCDs, read-out by appropriate electronics.
Recent developments

During 2016 we carried out 2 observational runs of 20 nights each with PAUcam with usual bad weather (only 30% of the nights were useful). This was April (16A) and Nov-Dec (16B). In Oct 2016 we perform a camera intervention. PAUcam was opened in the clean rooms of the GTC to replace the filter trays, obscure the camera to scatter light, and other maintenance and test. Data has been successfully reduced and process to start the science validation.

Recent publications
Cosmological constraints from multiple tracers in spectroscopic surveys Alarcon, A., Eriksen, M., & Gaztanaga, E. 2016, arXiv:1609.08510

Characterization and performance of PAUCam filters Casas, R., Cardiel-Sas, L., Castander, F.J., et al. 2016, PSPIE, 9908, 99084K

The PAU camera carbon fiber cryostat and filter interchange system Lopez, L., Padilla, C., Cardiel-Sas, L., et al. 2016, PSPIE, 9908, 99084G

The PAU camera at the WHT Padilla, C., Ballester, O., Cardiel-Sas, L., et al. 2016, PSPIE, 9908, 99080Z

Calibrating the PAU Survey's 46 Filters Bauer, A., Castander, F., Gaztanaga, E., et al. 2016, The Science of Calibration, 503, 99

Senior Institute members involved

E. Gaztañaga, F. Castander, M. Crocce, P. Fosalba
Institute of Space Sciences (IEEC-CSIC)

Campus UAB, Carrer de Can Magrans, s/n
08193 Barcelona.
Phone: +34 93 737 9788
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An institute of the Consejo Superior de Investigaciones Científicas

An institute of the Consejo Superior de Investigaciones Científicas
Affiliated with the Institut d'Estudis Espacials de Catalunya

Affiliated with the Institut d'Estudis Espacials de Catalunya