Euclid opens data treasure trove, offers glimpse of deep fields

(Press-News.org) Covering a vast sky area in three mosaics, the data release also includes numerous galaxy clusters, active galactic nuclei and transient phenomena. This first survey data unlocks a treasure trove of information for scientists to dive into and tackle some of the most intriguing questions in modern science. Euclid enables us to explore our cosmic history and the invisible forces shaping our universe.

With its exceptionally large field of view for a space telescope, capturing an area 240 times larger in a single shot than the Hubble Telescope, Euclid delivers outstanding image quality in both the visible and infrared light spectrum.

Crucial contributions from Germany

Euclid is particularly impressive in the infrared channel, for which the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching near Munich and the Max Planck Institute for Astronomy (MPIA) in Heidelberg provided critical components. After passing through four lenses, a filter, and a beam splitter, it achieves an extraordinarily high contrast. “The requirements for suppressing ghost images are exceeded by a factor of one hundred. The optical design and the precise execution of the optics at MPE and MPIA set new standards for image sharpness and contrast,” says Frank Grupp, who led the development of the near-infrared optics at MPE.

MPE is also contributing to research on galaxy evolution. “We have compiled a catalogue of over 70,000 spectroscopic redshifts from various sky surveys and combined it with the Euclid data,” explains Christoph Saulder, who led this part of the project. “This catalogue allows for precise distance measurements and the clear identification of numerous galaxies and quasars in Euclid’s high-resolution images. It serves as a foundation for a deeper understanding of these objects, their distribution, and their internal properties.”

“The new data are also being used to test the techniques for measuring cosmic shear and calibrating redshifts, which will soon be applied to the much larger Euclid data sets to achieve the primary scientific goal – the precision measurement of dark energy,” says Hendrik Hildebrandt from Ruhr University Bochum. He leads the key project for measuring cosmic shear and the redshift calibration task force.

Furthermore, scientists at Ludwig Maximilian University (LMU) in Munich have tested methods to identify and characterize galaxy overdensities, a crucial step in tracing the universe's large-scale structure. “The methodologies used to pinpoint galaxy clusters in this task will be key to fully exploiting Euclid’s vast dataset, improving cluster identification and contributing to a deeper understanding of cosmic structure formation. At the same time, they help explore previously uncharted regimes in the near-infrared with a statistically significant sample of objects,” says LMU scientist Barbara Sartoris.

Likewise, MPIA scientists play leading roles in numerous Euclid studies. They use the data to identify growing supermassive black holes, answer fundamental questions about galaxy evolution, and perform precise photometric measurements of young and old transient celestial objects.

Tracing out the cosmic web in Euclid’s deep fields



Euclid has scouted out the three areas in the sky where it will eventually provide the deepest observations of its mission. In just one week of observations and one scan of each region so far, Euclid spotted already 26 million galaxies. The most distant of those are up to 10.5 billion light-years away. The fields span a combined area equivalent to more than 300 times the full Moon.

In order to unravel the mysteries it is designed to explore, Euclid precisely measures the various shapes and the distribution of billions of galaxies with its high-resolution imaging visible instrument (VIS). In contrast, its near-infrared instrument (NISP) is essential for determining galaxy distances and masses.

MPE was responsible for designing and constructing the NISP near-infrared optics. In turn, MPIA carries out crucial tasks for NISP’s calibration. “MPIA engineers and scientists are developing and maintaining the mission’s entire calibration plan, calibrating and scientifically monitoring the near-infrared camera NISP, performing simulations, and conducting technical analyses such as instrument monitoring,” says MPIA’s Mischa Schirmer. He is the Euclid mission calibration and NISP calibration scientist.

The new images are a testimony to these efforts and showcase Euclid's capability of mapping hundreds of thousands of galaxies, and start to hint at the large-scale organization of these galaxies in the cosmic web.

Data processing and object classification



Euclid is expected to capture images of more than 1.5 billion galaxies over six years, sending back around 100 GB of data daily. Such an impressively large dataset creates incredible discovery opportunities, but also poses enormous challenges.

The Euclid consortium has established a European network of nine data centres, including the German Science Data Center (SDC-DE) at MPE. It is equipped with 7,000 processors and processes 10% of the data recorded by Euclid. A team of at least ten experts ensures smooth and consistent processing of astronomical imaging data. MPE’s Max Fabricius, who leads the SDC-DE, says: “Approximately 100 GB of raw data is processed virtually in real time every day. The demands on photometric precision are enormous and require a completely new approach to the methods used to calibrate the data.”

When it comes to searching for, analysing and cataloguing galaxies, the advancement of machine learning algorithms, in combination with thousands of human citizen science volunteers and experts, is playing a critical role. It is a fundamental and necessary tool to fully exploit Euclid’s vast dataset. A significant landmark in this effort is the first detailed catalogue of more than 380,000 galaxies, which have been characterized according to features such as spiral arms, central bars, and tidal tails that infer merging galaxies.

This first catalogue released today represents just 0.4% of the total number of galaxies of similar resolution expected to be imaged over Euclid’s lifetime. The final catalogue will present the detailed morphology of at least an order of magnitude more galaxies than ever measured before, helping scientists answer questions like how spiral arms form and how supermassive black holes grow.

Gravitational lensing discovery engine Light travelling towards us from distant galaxies is bent and distorted by normal and dark matter in the foreground. This effect is called gravitational lensing and is one of Euclid’s tools to reveal how dark matter is distributed throughout the universe. When the distortions are very apparent, it is known as ‘strong lensing’, which can result in features such as Einstein rings, arcs, and multiple imaged lenses.

A first catalogue of 500 galaxy-galaxy strong lens candidates is released today, almost all previously unknown. MPIA scientists were involved in gravitational lensing classifications, labelling images with markers according to their probability of being lenses, as input for machine learning. “These AI systems will ultimately be essential for analysing the 200 times larger sky area at the end of the mission. The number of galaxies distorted by lensing will eventually increase to a staggering 100,000, about 100 times more than currently known. Human classification of individual objects will not be possible for this unprecedented dataset,” emphasizes Knud Jahnke from MPIA. He is the NISP instrument scientist.

Euclid will also be able to measure ‘weak’ lensing, when the distortions of background sources are much smaller. Such subtle distortions can only be detected by statistically analysing large numbers of galaxies. In the coming years, Euclid will measure the distorted shapes of billions of galaxies over 10 billion years of cosmic history, thus providing a 3D view of the distribution of dark matter in our universe.

Background information As of 19 March 2025, Euclid has observed about 2000 square degrees, approximately 14% of the total survey area. The three deep fields together comprise 63.1 square degrees. 

Euclid ‘quick’ releases, such as the one of 19 March, are of selected areas. They are intended to demonstrate the data products expected in the major data releases that follow, and to allow scientists to sharpen their data analysis tools in preparation. The mission’s first cosmology data will be released to the community in October 2026. Data accumulated over additional, multiple passes of the deep field locations will be included in the 2026 release.

The data release of 19 March 2025 is described in multiple scientific papers that have not yet been through the peer-review process but will be submitted to the journal Astronomy & Astrophysics.

The University of Bonn hosts the Euclid Publication Office, where the scientific publications of the Euclid Consortium are coordinated and reviewed.

About Euclid Euclid was launched in July 2023 and started its routine science observations on 14 February 2024. It is a European mission, built and operated by the European Space Agency (ESA), with contributions from its member states and NASA. The Euclid Consortium – consisting of more than 2000 scientists from 300 institutes in 15 European countries, the USA, Canada, and Japan – is responsible for providing the scientific instruments and scientific data analysis. ESA selected Thales Alenia Space as prime contractor for constructing the satellite and its service module, with Airbus Defence and Space chosen to develop the payload module, including the telescope. NASA provided the detectors of the Near-Infrared Spectrometer and Photometer, NISP. Euclid is a medium-class mission in ESA’s Cosmic Vision Programme.

From Germany, the Max Planck Institute for Astronomy in Heidelberg, the Max Planck Institute for Extraterrestrial Physics in Garching, the Ludwig Maximilian University in Munich, the University of Bonn, the Ruhr University Bochum, the University of Bielefeld, and the German Space Agency at the German Aerospace Centre (DLR) in Bonn are participating in the Euclid project.

The German Space Agency at DLR coordinates the German ESA contributions and provides funding of 60 million euros from the National Space Programme for the participating German research institutes.

With around 21%, Germany is the most significant contributor to the ESA science programme.

This news item is based on an ESA press release that was published at the same time. Additional images are available via that release.

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