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ING research news release
23 Sep, 2024

The PAU Survey Data Release: a New Catalogue of Distant Galaxies with Unprecedented Distance Precision

The Physics of the Accelerating Universe Survey (PAUS) collaboration, led by the Spanish Institute of Space Sciences (ICE-CSIC), has announced the release of the PAUS data, a groundbreaking catalogue of cosmic distances derived from data obtained using the PAUCam camera on the William Herschel Telescope (WHT). This release will help astronomers to better understand how cosmic structures form, particularly under the influence of dark matter and dark energy.

The PAUS catalogue provides distances to 1.8 million galaxies with unprecedented precision over a field of view and depth never explored before. Covering a large sky area of 50 square degrees, similar to the size on sky of approximately 250 full moons, the PAUS data will allow astronomers to generate more accurate maps of the distribution of mass in the Universe. The PAUS catalogue is also a valuable resource for the astronomical community, contributing to the scientific analysis and calibration of other cosmological surveys.

The PAUS data were collected over 200 nights between 2015 and 2019 using the PAUCam imaging camera mounted on the prime focus of the WHT. PAUCam was specifically designed to accurately measure galaxy distances. The PAU Survey builds on existing deep images from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS), and the ESO Kilo-Degree Survey (KiDS). By combining these datasets, PAUCam can achieve a highly accurate distance determination for deep space objects.

The accelerated expansion of the Universe is attributed to dark energy, which constitutes about 70% of the Universe, yet its nature remains a mystery. The PAUS offers a new insight into this enigma, providing an accurate and comprehensive characterisation of millions of galaxies up to distances of more than 10 billion light years.

"The PAU Survey offers a groundbreaking approach to generating cosmic maps, made possible through the design and development of a novel instrument and a dedicated survey to collect and analyse data in ways never done before. It has been a privilege to collaborate with such a talented and dependable group," says Enrique Gaztañaga, Director of the PAUS Survey, and currently a Professor at the Institute of Cosmology and Gravitation at the University of Portsmouth, on leave from ICE-CSIC and the Institute of Space Studies of Catalonia (IEEC).

The ICE-CSIC, supported by the Spanish Ministry of Science, Innovation and Universities (MICIU), leads the PAUS collaboration, involving 14 institutions from 6 different countries. The ICE-CSIC was responsible for coordinating the observations, and they scientifically exploit the PAUS data in collaboration with IFAE, IEEC, PIC, IFT-UAM/CSIC, CIEMAT, Durham University, Ruhr-Universität Bochum, University College London, ETH Zurich, Leiden Observatory, University of Portsmouth and Tsinghua University.

The released PAUS data are available on the PAUS and CosmoHub websites, while the release itself is described in two papers on measuring distances and data calibration, published in the Monthly Notices of the Royal Astronomical Society (MNRAS).

The PAUcam camera installed at the prime focus of the WHT. Credit: PAUS team. Large format: PNG.

The PAUS catalogue represents a significant advancement in cosmological research, as it provides photometric redshift measurements that determine the distances of galaxies. To achieve this, the PAU camera employs 40 narrow-band optical filters, and the technique used involves imaging the same field multiple times through these narrow-band filters. As the Universe expands, the light emitted by distant astronomical objects shifts towards the red part of the spectrum. This shift, called "redshift", is crucial for measuring the distance to a distant object. PAUCam determines the redshifts of galaxies from the photometric information obtained in its narrow-band filters.

While ongoing and future state-of-the-art spectroscopic surveys make use of large telescope focal planes to simultaneously measure the redshifts of thousands of preselected galaxies, the PAUS takes a different approach. PAUS does not require preselecting target galaxies, and the data acquired through its 40 filters allow the determination of the redshifts of all the galaxies in the field of view at once, albeit at a lower spectral resolution.

"The precision in measuring galaxy distances depends on the number of filters used, as each filter provides different information about the observed galaxy. The great advantage of PAUS is that it combines information from 40 different filters, allowing for highly accurate distance measurements. This level of precision is essential for the study of the structure of the universe, which in turn requires data from a large number of galaxies", says David Navarro-Gironés, PhD student at ICE-CSIC and member of the PAUS team.

The PAU survey provides complete, flux-limited, and highly accurate redshift and spectral energy distributions of millions of astronomical objects, reaching a depth and coverage previously unexplored.

This map shows the position on sky of approximately 750,000 galaxies in one of the four PAUS fields (W3 CFHT-Lens). The colour represents the mean redshift (z) of galaxies in each pixel, with z indicating both cosmic distance and time. For instance, galaxies at z ~0.9 (yellow) emitted light about 7.4 billion years ago, or when the universe was about half its size today. Empty regions correspond to bright foreground objects (bright stars or galaxies). This map provides valuable insights into the large-scale structure of the universe, supporting studies of galaxy evolution, dark matter and dark energy. Credits: CosmoHub.com. Large format: PNG.

About the PAU Survey

The foundations of the PAUS project were laid around 2007 as part of the Consolider Ingenio 2010 initiative, funded by the Spanish government. The Spanish groups involved continued the project, building PAUCam for its use at the WHT, and starting the PAUS collaboration for the analysis of the data.

"Starting a collaboration of several Spanish groups and continuing it with a very ambitious instrument, despite rather limited material and human resources, was not without risk. However, the fact is that the camera performed well almost from first light. Equally remarkable is that six European and one Chinese group joined PAUS for data analysis, contributing with their own resources", says Enrique Fernández, from IFAE and UAB (Universitat Autónoma de Barcelona), who led the PAU Consolider Project and the PAUS collaboration during the first years.

The PAU Survey is an extensive international collaboration involving institutions from Spain, the United Kingdom, the Netherlands, Switzerland, Germany and China. The scientific exploitation of the PAUS data — including observations, data reduction and calibration, simulations, photometric redshift, and clustering analysis — has been led by ICE-CSIC alongside the Institut de Física d'Altes Energies (IFAE) and other Spanish institutions such as the Port of Scientific Information (PIC), the Institute of Space Studies of Catalonia (IEEC), the Instituto de Física Teórica (IFT-UAM/CSIC), and the Research Centre for Energy, Environment and Technology (CIEMAT).

The construction and integration of PAUCam was entirely carried out by IFAE in Barcelona, in partnership with ICE-CSIC, PIC, IEEC, CIEMAT, and IFT-UAM/CSIC.

The ICE-CSIC was responsible for the camera design, and the optical bench design and construction, and it also played an important role in writing the software for the data reduction, calibration, automated analysis using pipelines, and the data dissemination, working closely with PIC, which serves the PAUS data centre.

CIEMAT was responsible, for the design, production, testing and installation of the full PAUCam electronics, together with IFAE. CIEMAT also carried out the testing and validation of the filters and the production and installation of several mechanical parts of the camera.

The commissioning and first light of PAUCam on the WHT were achieved by the Spanish groups listed above in 2015, with invaluable assistance from the ING engineers who have also been collaborating with the PAUCam team since 2009. Following this milestone, an international collaboration was started in 2015, including Durham University (United Kingdom), Leiden Observatory (the Netherlands), Ruhr-Universität Bochum (Germany), University College London (UCL, the United Kingdom), ETH Zurich (Switzerland), the Institute of Cosmology and Gravitation at the University of Portsmouth (United Kingdom), and Tsinghua University (China). These institutions made contributions to funding, human resources and expertise, playing a crucial role in the successful exploitation of the PAU survey.

The PAUS team members from Leiden, UK, and Spain secured the necessary observing time by successfully competing in 10 different time allocation calls between 2015 and 2019. Additionally, external groups had the opportunity to use PAUCam as a visitor instrument in several observational campaigns.

Nine years after its first light in 2015, the PAU survey reached a remarkable milestone, measuring the distances of almost 2 million distant galaxies with a relative precision of just 0.3%. The team is currently using these data to enhance the calibration of existing cosmological surveys. For instance, PAUS data is being used to improve weak lensing analyses and simulations for dark energy missions such as ESA's Euclid mission and the Rubin Observatory's Legacy Survey of Space and Time (LSST). Additionally, these samples can refine the redshift distributions for such missions, as has already been done for KiDS and the Dark Energy Survey (DES).

"In addition to high-precision redshifts, the 40 narrow-band filters of PAUCam offer a unique window into the evolution and environment of galaxies. With PAUS, we can directly observe strong emission lines and spectral breaks, usually reserved to slower and more expensive spectroscopic surveys. These observations allow us to better constrain the age and composition of galaxies, identify quasars with high accuracy, and may even provide a window into the diffuse gas clouds around and between galaxies", says Pablo Renard, a postdoctoral fellow at Tsinghua University and currently PAUS Data Manager.

In the coming months, the team will also present an ongoing study on galaxy clustering and intrinsic galaxy shape alignments, contributing to a deeper understanding of how our universe formed and evolved.


About the William Herschel Telescope

The Willliam Herschel Telescope (WHT) is operated on the island of La Palma by the Isaac Newton Group of Telescopes (ING) in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias (IAC). The ING is funded by the Science and Technology Facilities Council (STFC-UKRI) of the United Kingdom, the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) of the Netherlands, and the IAC in Spain. IAC's contribution to the ING is funded by the Spanish Ministry of Science, Innovation and Universities.


Related publications

D. Navarro, E. Gaztañaga, M. Crocce, A. Wittje et al, 2024, "The PAU Survey: Photometric redshift estimation in deep wide fields", MNRAS, DOI: 10.1093/mnras/stae1686. [Paper]

F. Castander, S. Serrano, M. Eriksen, E. Gaztañaga et al, 2024, "The PAU survey: photometric calibration of narrow band images. Monthly Notices of the Royal Astronomical Society", MNRAS, DOI: 10.1093/mnras/stae1507. [Paper]


More information

"Publican un nuevo catálogo de distancias cósmicas para desvelar los misterios de la formación del universo", CSIC press release, 18th September 2024.

"The PAUS survey releases a new cosmic distance catalogue to unlock the mysteries of the Universe formation", ICE press release, 18th September 2024.

"The PAUS survey releases a new cosmic distance catalogue to unlock the mysteries of the Universe formation", IFAE press release, 18th September 2024.

"The PAUS survey releases a new cosmic distance catalogue to unlock the mysteries of the Universe formation", IEEC press release, 18th September 2024.

The PAUS data are available on the public data release web pages.

The PAU Survey site.

PAUCam on the ING website.


Contacts

Enrique Gaztañaga
Director of the PAUS Survey
e.gaztanagacsic.es

Javier Méndez
ING PR Officer
outreaching.iac.es



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