New catalog of cosmic distances to reveal the mysteries of the formation of the universe

S has publicly presented a pioneering catalog of cosmic distances. This catalog includes data collected during 200 nights between 2015 and 2019 using the PAUCam camera of the William Herschel Telescope (WHT), on La Palma, in the Canary Islands of Spain.

The catalog has been published on the PAUS (Physics of the Accelerating Universe Survey) project website and on the CosmoHub portal.

PAUS is an international collaboration led by the Institute of Space Sciences (ICE), dependent on the Higher Council for Scientific Research (CSIC) in Spain, in which 14 institutions from 6 countries participate.

In addition, the catalog of cosmic distances is detailed in two studies published in the academic journal Monthly Notices of the Royal Astronomical Society (MNRAS): one on the measurement of distances and another on the calibration of PAUS data. The team that carried out the first study is headed by David Navarro-Gironés, a predoctoral researcher at ICE. The second study is the work of a team headed by Francisco Castander, from ICE as well as the Institute of Spatial Studies of Catalonia (IEEC). The first study is titled “The PAU Survey: Photometric redshift estimation in deep wide fields”. The second is titled “The PAU survey: photometric calibration of narrow band images”.

This new catalog provides information on millions of distant galaxies, determining their distances with unprecedented precision, with a field of view and depth never before explored. The mapping covers a wide area of ​​sky of 50 square degrees, similar to an area of ​​approximately 250 full moons, encompassing data on 1.8 million astronomical objects. This deeper look will allow more precise maps to be created to determine how exactly the matter structure of the universe formed, and also to find out what dark matter and dark energy are.

The PAUCam camera was specially designed to accurately measure distances to galaxies, allowing the expansion of the universe to be studied under the influence of dark matter and dark energy.

The project is based on existing deep images from the CFHTLenS (Canada-France-Hawaii Telescope Lensing Survey) mapped by the CFH (Canada-France-Hawaii) telescope in Hawaii, and the KiDS (Kilo-Degree Survey) carried out with the VST telescope (VLT Survey Telescope) in Chile, which belongs to the European Southern Observatory (ESO). By combining these data sets, the PAUS project has obtained very precise information about the distance and time of deep space objects.

The accelerated expansion of the universe is attributed to dark energy, which makes up about 70% of the universe, but its nature remains unknown. PAUS mapping can help clarify this enigma, as it provides an accurate and complete characterization of millions of galaxies located up to distances of more than 10 billion light-years from us. This catalog is a valuable resource for the astronomical community by contributing to the scientific analysis and calibration of other cosmological maps.

“PAUS mapping offers a revolutionary approach to cosmic mapping, made possible by the design and development of a novel instrument and mapping dedicated to collecting and analyzing data in ways that have never been done before. It has been a privilege to collaborate with such a talented and reliable group,” says Enrique Gaztañaga, director of PAUS mapping, which began in 2015, and currently professor at the Institute of Cosmology and Gravitation at the University of Portsmouth in the United Kingdom, on leave from ICE and the Institute of Spatial Studies of Catalonia (IEEC).

A milestone in cosmic research

This catalog represents a significant advance in cosmic research, providing photometric redshift measurements that determine distances to galaxies as they appeared billions of years ago. To obtain these measurements, the PAU camera uses 40 filters of different colors that represent narrow bands in the optical spectrum. This technique involves photographing the same field several times through various color filters. As objects move away from us, the light they emit undergoes a redshift, moving toward the red end of the spectrum. In astronomy, redshift is crucial for calculating the distance of an object from Earth.

While current and future next-generation cosmic spectroscopic surveys are equipped with large focal planes that allow simultaneous measurement of the redshifts of thousands of preselected galaxies—acquiring hundreds of galaxy redshifts per square degree in a single observation of a total of approximately 30,000 galaxies at the desired depth limit—the PAUS survey takes a different approach. This project does not require preselecting galaxies. Instead, it uses its 40 filters to measure the redshifts of all 30,000 galaxies within the field of view at once, albeit with lower spectral resolution.

“The precision when measuring galaxy distances depends on the number of filters used, since each filter provides different information about the galaxy. The great advantage of PAUS is that it combines information from 40 different filters, allowing highly accurate distance measurements to be made. This level of precision is crucial for the study of the structure of the universe, which in turn requires data from a large number of galaxies,” says David Navarro-Gironés, predoctoral researcher at ICE and first author of one of the two new studies. .

PAUS mapping provides comprehensive, high-precision flux range information on the redshift and spectral energy distribution of millions of galaxies and stars, reaching a depth and area previously unexplored. This is achieved without the need to select a series of specific objectives, which is a powerful tool to better understand sample selection and the integrity of astronomical mapping.

PAUCam camera installed at the primary focus of the William Herschel telescope, on La Palma. (Photo: PAUS)

International contribution to PAUS mapping

An international collaboration between Spain, the United Kingdom, the Netherlands, Switzerland, Germany and China has made PAUS mapping possible. The scientific exploitation of the new catalog data—including observations, data reduction and calibration, simulations, photometric redshift, and galaxy clustering analysis—has been led by ICE, together with the Institute of High Energy Physics (IFAE). ) in Bellaterra, Barcelona. The PIC (Port d’Informació Cientifica) of Bellaterra, Barcelona (managed by the IFAE and the CIEMAT), the IEEC, the Institute of Theoretical Physics (IFT) and the Center for Energy, Environmental and Technological Research (CIEMAT) have also collaborated. .

The construction and integration of the PAU chamber was carried out entirely in Barcelona, ​​​​under the direction of the IFAE in collaboration with the ICE, the PIC, the IEEC, the CIEMAT and the IFT (of the CSIC and the Autonomous University of Madrid (UAM )).

In addition to assisting in the design of the camera, optical bench and construction, ICE also played a key role in data reduction, calibration, automated analysis processes and data distribution, working closely with the PIC, which acts as PAUS’ data centre, alongside the wider PAUS team. CIEMAT was responsible, together with IFAE, for the design, production, testing and installation of all PAUCam electronics. CIEMAT was also responsible for testing and validation of the filters and for the production and installation of various mechanical parts of the chamber.

The commissioning and first light of PAUCam on the 4.2 meter WHT telescope took place in 2015 by these groups in Spain, with the invaluable help of the WHT engineering staff, the Isaac Newton Telescope Group (ING ), in La Palma. Following this milestone, an international collaboration was formed in 2015, including Durham University (UK), Leiden Observatory (Netherlands), Ruhr University Bochum (Germany), University College London (UK United Kingdom), the Swiss Federal Institute of Technology in Zurich (ETH), the Institute of Cosmology and Gravitation at the University of Portsmouth (United Kingdom) and Tsinghua University (China).

Nine years after its first light, in 2015, PAUS has reached a milestone: it has measured the distances of numerous distant galaxies with a relative precision of 0.3%. The team is currently using this data to improve the calibration of existing cosmological surveys. For example, PAUS data is being used to improve weak gravitational lensing analyzes and simulations for space missions studying dark energy, such as ESA’s Euclid mission and the Rubin Observatory’s Legacy Survey of Space and Time (LSST). . Furthermore, these samples can refine the redshift distributions for such missions, as has already been done for the KiDS and DES (Dark Energy Survey) scientific collaborations.

“In addition to high-precision redshifts, PAUS’s 40 narrowband filters offer a unique window into the evolution and environment of galaxies. With PAUS, we can directly observe intense emission lines and spectral discontinuities, something normally reserved for slower and more expensive spectroscopic studies. These observations allow us to better delineate the age and composition of galaxies, identify quasars with great precision, and can even provide a window into the diffuse gas clouds that exist around and between galaxies,” says Pablo Renard, postdoctoral researcher at the University of Tsinghua and currently chief data officer of PAUS.

In the coming months, the team will also present a study currently in development on the clustering of galaxies and the intrinsic characteristics of their shape, contributing to a better understanding of how our universe formed and evolved. (Source: Alba Calejero / ICE / CSIC)