Euclid delivers first scientific results

ESA’s space telescope reveals secrets of the cosmos. University of Bonn is involved

Euclid’s image of the galaxy cluster Abell 2390 - shows more than 50,000 g
Euclid’s image of the galaxy cluster Abell 2390 - shows more than 50,000 galaxies and a beautiful representation of gravitational lensing. This image section corresponds to just about a tenth of the entire Euclid image field, which is about twice the size of the full moon. Image: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre, G. Anselmi; CC BY-SA 3.0 IGO all’images in original size .
Today, the Euclid Consortium publishes the first scientific publications on observations with the Euclid space telescope. In a first early observation phase, some scientifically spectacular results have already been achieved. These give a glimpse of the unprecedented capabilities of the telescope, which is expected to produce over the next few years one of the most accurate maps of the evolution of our Universe. All fifteen publications will be available on the arXiv preprint server from tomorrow on. Once the peer review process is complete, they will also appear in a special issue of the journal "Astronomy & Astrophysics."

The discovery of free-flying, new-born planets, the study of the globular cluster population of nearby galaxies, the discovery of new faint and dwarf galaxies in nearby galaxy clusters, the distribution of dark and luminous matter between the galaxies of galaxy clusters and the study of distant galaxies magnified by gravitational lensing are described in a series of ten publications. At the same time as these initial scientific results, the Euclid Consortium is today publishing the technical foundations of the mission in five comprehensive articles. These demonstrate the outstanding qualities of Euclid and will serve as a reference for the analysis of Euclid data for years to come.

All publications have already been reviewed and discussed in advance by the Consortium, in order to ensure a uniform apprearance and a consistently high level of quality for each publication even before it is submitted for journal review. For this purpose, the Euclid Consortium operates its own Editorial Office, which is based at the Argelander Institute for Astronomy (AIfA) at the University of Bonn under the chairmanship of Prof. Peter Schneider. The coordinated simultaneous submission of fifteen articles, with up to more than a thousand authors, presented a particular challenge. Patrick Simon, who is in charge of the Editorial Office, is delighted: "With this set of publications, Euclid is finally presenting itself to the wider scientific public. The reference publications provide a comprehensive description of all’aspects of the mission, and the initial analysis of the data paints an impressive picture of Euclid’s scientific potential."

Reference publications

An overview article describes the scientific objectives of the Euclid mission, the technical details of the satellite, the observation plan, the data products, the plans for data analysis and the expected results. This article is the reference for anyone interested in the Euclid data and scientific results. Yannick Mellier, lead of the Euclid Consortium, underlines: "This paper summarizes all the outstanding results of more than ten years of development. Euclid is already exceeding our expectations and will be at the forefront of exploring not only the dark universe, but almost all’areas of astronomy."

Three publications describe in detail the specifications, design, development and roles of Euclid’s scientific instruments. The VIS camera (for "visual") is a 609-megapixel camera that works in visible light; the NISP instrument (for "near-infrared spectrometer and photometer") images infrared light in several wavelength ranges and can also observe spectroscopically. The combination of these two cameras represents Euclid’s core competence. Initial tests have shown that both instruments fully meet expectations. Over the coming years, they will provide excellent data to map the large-scale structure in the Universe and its evolution. This will help, for example, to further investigate the nature of dark energy or to test the validity of the general theory of relativity at large distances.

The fifth publication describes the "Flagship" galaxy catalog, a simulated catalog of billions of galaxies. This is based on the Euclid Consortium’s Flagship simulation, the largest cosmological simulation ever carried out. Originally developed to prepare and test the scientific analysis of the Euclid data in advance of the mission launch, these simulations are now being used to identify and correct potential systematic errors in the data.

First scientific images, analyses and publications

During the first months of the Euclid mission, while still in the testing and commissioning phase, a few selected targets were observed to demonstrate the brilliance of the images and the diverse scientific potential of the Euclid data. A total of twenty-four hours were spent on these early observations. Five images were already published in November 2023, and ESA is releasing another set today, on May 23, 2024.

The Euclid Consortium has already been able to carry out an initial scientific analysis of some of these early observations ("Early Release Observations", ERO). The results of these investigations are being made available to the public today and demonstrate the wide variety of astronomical investigations that Euclid will make possible.

Free-flying, newly formed planets were discovered in star-forming regions; the structure of selected globular clusters in the Milky Way was measured down to the outer fringes; the detailed morphology and composition of some nearby galaxies were investigated; the distribution of globular clusters in the Fornax galaxy cluster was measured with unprecedented accuracy. The investigation of the nearby Perseus galaxy cluster led to a doubling of the known dwarf galaxies and to the discovery that stars and globular clusters in the space between the galaxies contribute one third of the cluster’s luminosity. The observation of two gravitational lensing clusters led not only to the discovery of highly distorted background objects, but also to the identification of twenty-nine candidates for galaxies from the earliest epoch of our Universe.

"The performance of Euclid is demonstrated by the combination of the extraordinarily large field of view, the very stable optics and the broad spectral coverage from the optical to the near-infrared. This allows us to capture a wide variety of objects and scales in a single image. The ERO only give a small hint of the results to be expected from the Euclid mission," emphasizes Reiko Nakajima from the AIfA at the University of Bonn, who is the instrument scientist responsible for the image quality of the VIS instrument. In fact, all these spectacular observations have been made within a short period of time, which is less than 0.1% of the total planned observation time of Euclid.

All fifteen publications will be published tomorrow on the arXiv preprint server. After completion of the peer review process, they will also appear in a special issue of the journal "Astronomy & Astrophysics." The ERO images will be made available for download by ESA together with the original data.

Future milestones planned for the Euclid mission

The next planned data releases of the Euclid Consortium will focus on the core objectives of the project: A first public access to the regular scientific data will be possible with a "quick release" in spring 2025; data from the first year of the regular observing program, which will eventually cover a third of the entire sky, is scheduled to become public in summer 2026. Further data releases in the following years will then successively make the respective progress in the project publicly accessible, until the completion of the nominal observation program in 2031.

The Euclid Consortium

Together with the European Space Agency (ESA), the Euclid Consortium is responsible for the planning, construction and operation of the Euclid space telescope. The aim of the project is to map the darkest regions of the sky over a period of six years. In particular, the comprehensive data should provide new insights into the nature of dark energy and dark matter. The telescope was successfully launched into space on 1 July 2023 and began its regular observation program on 14 February 2024 after a roughly six-month commissioning phase.

The Euclid Consortium consists of more than 2,600 members, including more than 1,000 active scientists from over 300 research institutes in 15 European countries as well as Japan, Canada and the USA.