The PAU Survey

Enrique Fernández

Physics of the Accelerating Universe Survey (PAUS) is an ongoing extragalactic survey carried out with the William Herschel Telescope in La Palma, Canary Islands, equipped with the PAUCam Camera. PAUS originated in the context of the PAU Project funded by the Consolider Ingenio 2010 Program of the Spanish Ministry of Research and Innovation.


The PAU project was approved in 2007 and ended in 2014. The main deliverable of the project was the PAUCam camera, operated as a Visitor’s Instrument at the prime focus of the William Herschel Telescope in the Canary Island of La Palma by the PAUCam Group, formed by 5 of the 7 groups originally in the Consolider Project, from CIEMAT and IFT (in Madrid), and from IEEC, PIC and IFAE (in Barcelona). These are the groups that also built the PAUCam and its software and also collaborate closely in other projects such as DES and DESI, described elsewhere in this report. Starting in 2016 other groups have joined the PAUS Collaboration, namely from Durham University and University College of London in the UK, from Leiden Observatory in the Netherlands, from ETH in Zurich, Switzerland, and from Bonn University in Germany.
Figure 1:

First scientific results

2018 has been an important year for PAUS as the first scientific results coming from the project have been published in scientific journals. Some of these publications are:

  • The PAU Survey: Early demonstration of the photometric redshift performance in the COSMOS field. This is an important paper that shows that PAUS meets its design goals. The comparison to secure spectra from zCOSMOS shows that PAUS achieves $\sigma_68 / (1+z) = 0.0037$ to $i_AB < 22.5$ when selecting the best 50% of the sources based on a photometric redshift quality cut. Furthermore, a higher photo-z precision of ($\sigma_68/(1 + z) _ 0.001$) is obtained for a bright and high-quality selection, which is driven by the identification of emission lines (see Fig. 2).
Figure 2: The $\sigma_ {68}/(1+z)$ (top) and outlier fraction (bottom) for different quality cuts as a function of the cumulative magnitude bins. The solid lines show the results when 100, 80, 50 and 20 percent of the sample remains after a quality cut. The dashed line shows the COSMOS results without any quality cuts, using the public COSMOS2015 catalog.

  • The Physics of the Accelerating Universe Camera (accepted by the Astronomical Journal). This paper describes with some detail the design, construction and first operations of PAUCam, including its control system. Fig. 3 shows the comparison of two spectra measured by PAUS and SDSS, which indeed agree very well.

  • The PAU Survey: Operation and orchestration of multi-band survey data (submitted to Astronomy and Computing). Together with the camera and its control software, a whole software system was also developed to treat the data, from its transfer from the telescope to the PAUS data center (located at PIC) to the deliver of science ready data to the PAUS collaboration. Particularly important is the PAUS database, developed for the coordination of the different computing tasks and to preserve and guarantee the consistency of data and metadata.

Other publications are listed in the list of publications.

Figure 3: Spectral energy distributions of a QSO (top panel) and an emission line galaxy (bottom panel). Emission lines are clearly detected in both objects. The PAUCam measured fluxes are marked with circles while the SDSS spectra, binned at the narrow band resolution, are shown with a solid line. The PAUCam and SDSS fluxes are in very good agreement.