Euclid opens a treasure trove of data: How MPE researchers explore the dark universe

The first Euclid data published by ESA (Q1) provide impressive insights into the depths of the universe. They include high-resolution images of 26 million galaxies, reveal the finest structures and make it possible for the first time to precisely determine the shape and distance of more than 380,000 galaxies. This data is a milestone and yet only marks the beginning of research into dark matter and dark energy. And the Max Planck Institute for Extraterrestrial Physics (MPE) plays a central role in all of this.

With its exceptionally large field of view, Euclid covers an area 240 times larger than the Hubble telescope in a single exposure, and delivers outstanding image quality in both visible and infrared light. Euclid's near-infrared capabilities are particularly impressive thanks to the near-infrared optics of the NISP instrument, which was developed and built mainly at MPE. The instrument consists of four lenses, a filter and a beam splitter. "The requirements for the suppression of ghost images are exceeded by a factor of one hundred. The optical design and the precision of the optics set new standards in terms of image resolution and contrast," says Frank Grupp, who led the development of NISP.

Another important role of MPE is the processing of Euclid data. Together with the Max Planck Computing and Data Facility (MPCDF), it operates the German Science Data Centre (SDC-DE) on the Garching campus, one of nine European data centres, which uses 7,000 processors to handle about 10 percent of the data recorded by Euclid. "Every day, about 100 gigabytes of raw data are processed in near-real time. The demands on photometric precision are enormous and require completely new methods of data calibration," explains Max Fabricius, who leads the SDC-DE.

A particular focus lies on the development of new methods to analyse the data and to meet the extremely high quality requirements, especially with regard to the photometric precision of the Euclid mission. Continuous testing, adaptation and innovation of the algorithms and technical infrastructure are essential.

A system administrator and two scientific IT specialists are responsible for maintaining and optimising the computer cluster and for adapting and deploying the highly specialised Euclid software. In addition, the SDC-DE plays a crucial role in providing the ground-based imaging data needed to determine high-precision photometric redshifts.

Research into galaxy evolution

MPE scientists Christoph Saulder and Roberto Saglia are working on redshifts. "We have created a catalogue of more than 70,000 spectroscopic redshifts from many different sky surveys and combined it with the Euclid data," says Christoph Saulder, who led this part of the project. "This catalogue allows accurate distance determination and correct identification of many galaxies and quasars in the high-resolution Euclid imaging data, and provides the basis for a precise understanding of these objects, their abundance and internal properties".

The catalogue has also been used to test the photometric redshifts obtained from the Euclid data itself. To ensure the highest possible quality of the photometric redshifts, the two scientists examined the Q1 data to optimise the calculation of the photometric redshifts. Ariel Sanchez and his team are studying the large-scale distribution of galaxies and voids - vast, almost matter-free regions of the Universe. Their goal is to develop new methods to precisely study the effects of dark energy on the structure of the universe.

12,000 active supermassive black holes discovered

Finally, the Euclid data will also provide new insights into X-ray astronomy. William Roster and Mara Salvato analysed the Q1 data set, focusing on active galactic nuclei (AGN). These are galaxies with active supermassive black holes at their centres. They identified a total of 12,000 AGN and countless other X-ray sources.

"This sample is significant," says Roster, "because for the first time we can combine deep, homogeneous near-infrared data with X-ray observations. This opens up new possibilities for discovering rare and elusive AGN, including highly obscured and high-redshift objects. Mara Salvato is thrilled about the future: "The insights from these observations will be of great importance for the analysis of future Euclid data sets - and we are very excited to see what new discoveries await us!"

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.