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\t\t\t\t\t\t19\/03\/2025<\/span> On 19 March 2025, the European Space Agency\u2019s Euclid mission released its first batch of survey data, including a preview of its deep fields. Here, hundreds of thousands of galaxies in different shapes and sizes take centre stage and show a glimpse of their large-scale organisation in the cosmic web.<\/b><\/p>\n<\/div>\n Covering a huge area of the sky in three mosaics, the data release also includes numerous galaxy clusters, active galactic nuclei and transient phenomena, as well as the first classification survey of more than 380 000 galaxies and 500 gravitational lens candidates compiled through combined artificial intelligence and citizen science efforts. All of this sets the scene for the broad range of topics that the dark Universe detective Euclid is set to address with its rich dataset.<\/p>\n \u201cEuclid shows itself once again to be the ultimate discovery machine. It is surveying galaxies on the grandest scale, enabling us to explore our cosmic history and the invisible forces shaping our Universe,\u201d says ESA\u2019s Director of Science, Prof. Carole Mundell.<\/p>\n \u201cWith the release of the first data from Euclid\u2019s survey, we are unlocking a treasure trove of information for scientists to dive into and tackle some of the most intriguing questions in modern science. With this, ESA is delivering on its commitment to enable scientific progress for generations to come.\u201d<\/p>\n<\/p><\/div>\n 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, with one scan of each region so far, Euclid already spotted 26 million galaxies. The farthest of those are up to 10.5 billion light-years away.<\/p>\n The fields also contain a small population of bright quasars that can be seen much farther away. In the coming years, Euclid will pass over these three regions tens of times, capturing many more faraway galaxies, making these fields truly \u2018deep\u2019 by the end of the nominal mission in 2030.\u00a0<\/p>\n But the first glimpse of 63 square degrees of the sky, the equivalent area of more than 300 times the full Moon, already gives an impressive preview of the scale of Euclid\u2019s grand cosmic atlas when the mission is complete. This atlas will cover one-third of the entire sky \u2013 14 000 square degrees \u2013 in this high-quality detail.<\/p>\n<\/p><\/div>\n \u201cIt\u2019s impressive how one observation of the deep field areas has already given us a wealth of data that can be used for a variety of purposes in astronomy: from galaxy shapes, to strong lenses, clusters, and star formation, among others,\u201d says Valeria Pettorino, ESA\u2019s Euclid project scientist. \u201cWe will observe each deep field between 30 and 52 times over Euclid\u2019s six year mission, each time improving the resolution of how we see those areas, and the number of objects we manage to observe. Just think of the discoveries that await us.\u201d<\/p>\n<\/p><\/div>\n To answer\u00a0the mysteries it is designed for, Euclid measures the huge variety of shapes and the distribution of billions of galaxies very precisely with its high-resolution imaging\u00a0visible instrument (VIS), while its near-infrared instrument (NISP)\u00a0is essential for unravelling galaxy distances and masses. The new images already showcase this capability for hundreds of thousands of galaxies, and start to hint at the large-scale organisation of these galaxies in the\u00a0cosmic web. These filaments of ordinary matter and dark matter weave through the cosmos, and from these, galaxies formed and evolved. This is an essential piece in the puzzle towards understanding the\u00a0mysterious nature of dark matter and dark energy, which together appear to make up 95% of the Universe.\u00a0<\/p>\n \u201cThe full potential of Euclid to learn more about dark matter and dark energy from the large-scale structure of the cosmic web will be reached only when it has completed its entire survey. Yet the volume of this first data release already offers us a unique first glance at the large-scale organisation of galaxies, which we can use to learn more about galaxy formation over time,” says Clotilde Laigle, Euclid Consortium scientist and data processing expert based at the Institut d’Astrophysique de Paris, France.<\/p>\n<\/p><\/div>\n Euclid is expected to capture images of more than 1.5 billion galaxies over six years, sending back around 100 GB of data every day. Such an impressively large dataset creates incredible discovery opportunities, but huge challenges when it comes to searching for, analysing and cataloguing galaxies. The advancement of artificial intelligence (AI) algorithms, in combination with thousands of human citizen science volunteers and experts, is playing a critical role.\u00a0<\/p>\n \u201cWe\u2019re at a pivotal moment in terms of how we tackle large-scale surveys in astronomy. AI is a fundamental and necessary part of our process in order to fully exploit Euclid\u2019s vast dataset,\u201d says Mike Walmsley, Euclid Consortium scientist based at the University of Toronto, Canada, who has been heavily involved in astronomical deep learning algorithms for the last decade.<\/p>\n \u201cWe\u2019re building the tools as well as providing the measurements. In this way we can deliver cutting-edge science in a matter of weeks, compared with the years-long process of analysing big surveys like these in the past,\u201d he adds.<\/p>\n A major milestone in this effort is the first detailed catalogue of more than 380 000 galaxies, which have been classified according to features such as spiral arms, central bars, and tidal tails that infer merging galaxies. The catalogue is created by the \u2018Zoobot\u2019 AI algorithm.\u00a0During an intensive one-month campaign on Galaxy Zoo last year, 9976 human volunteers worked together to teach Zoobot to recognise galaxy features by classifying Euclid images.\u00a0<\/p>\n<\/p><\/div>\n This first catalogue released today represents just 0.4% of the total number of galaxies of similar resolution expected to be imaged over Euclid\u2019s 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.\u00a0<\/p>\n \u201cWe\u2019re looking at galaxies from inside to out, from how their internal structures govern their evolution to how the external environment shapes their transformation over time,\u201d adds Clotilde.<\/p>\n \u201cEuclid is a goldmine of data and its impact will be far-reaching, from galaxy evolution to the bigger-picture cosmology goals of the mission.\u201d<\/p>\n<\/p><\/div>\n Light travelling towards us from distant galaxies is bent and distorted by normal and dark matter in the foreground. This effect is called\u00a0gravitational lensing\u00a0and it is one of the tools that Euclid uses to reveal how dark matter is distributed through the Universe.<\/p>\n When the distortions are very apparent, it is known as \u2018strong lensing\u2019, which can result in features such as\u00a0Einstein rings, arcs, and multiple imaged lenses.<\/p>\n Using an initial sweep by AI models, followed by citizen science inspection, expert vetting and modelling, a first catalogue of 500 galaxy-galaxy strong lens candidates is released today, almost all of which were previously unknown.\u00a0This type of lensing happens when a foreground galaxy and its halo of dark matter act as a lens, distorting the image of a background galaxy along the line of sight towards Euclid.\u00a0<\/p>\n<\/p><\/div>\n With the help of these models, Euclid will capture some 7000 candidates in the major cosmology data release planned for the end of 2026, and in the order of 100 000 galaxy-galaxy strong lenses by the end of the mission, around 100 times more than currently known.<\/p>\n Euclid will also be able to measure\u00a0\u2018weak\u2019 lensing, when the distortions of background sources are much smaller. Such subtle distortions can only be detected by analysing large numbers of galaxies in a statistical way. 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.<\/p>\n \u201cEuclid is very quickly covering larger and larger areas of the sky thanks to its unprecedented surveying capabilities,\u201d says Pierre Ferruit, ESA\u2019s Euclid mission manager, who is based at ESA\u2019s\u00a0European Space Astronomy Centre (ESAC)\u00a0in Spain, home of the\u00a0Astronomy Science Archive\u00a0where Euclid\u2019s data will be made available.<\/p>\n \u201cThis data release highlights the incredible potential we have by combining the strengths of Euclid, AI, citizen science and experts into a single discovery engine that will be essential in tackling the vast volume of data returned by Euclid.\u201d<\/p>\n Notes to editors<\/b><\/p>\n As of 19 March 2025, Euclid has observed about 2000 square degrees, approximately 14% of the total survey area (14 000 square degrees). The three deep fields together comprise 63.1 square degrees.\u00a0<\/p>\n Euclid \u2018quick\u2019 releases, such as the one of 19 March, are of selected areas, intended to demonstrate the data products to be expected in the major data releases that follow, and to allow scientists to sharpen their data analysis tools in preparation. The mission\u2019s 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.<\/p>\n The three deep field previews can now be explored in ESASky from 19 March 12:00 CET onwards:<\/p>\n The data release of 19 March 2025 is described in multiple scientific papers which have not yet been through the peer-review process, but which will be submitted to the journal Astronomy & Astrophysics. A preprint of the papers is available here from 19 March 12:00 CET.<\/p>\n Find more detailed information about the data release here.<\/p>\n About Euclid\u00a0<\/b><\/p>\n Euclid was launched in July 2023 and started its routine science observations on 14 February 2024. In November 2023 and May 2024, the world got its first glimpses of the quality of Euclid\u2019s images, and in October 2024 the first piece of its great map of the Universe was released.<\/p>\n Euclid is a European mission, built and operated by ESA, with contributions from its Member States and NASA. The Euclid Consortium \u2013 consisting of more than 2000 scientists from 300 institutes in 15 European countries, the USA, Canada and Japan \u2013 is responsible for providing the scientific instruments and scientific data analysis. ESA selected Thales Alenia Space as prime contractor for the construction of 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\u2019s Cosmic Vision Programme.<\/p>\n Contact<\/b><\/p>\n \nESA Media relations
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\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nTracing out the cosmic web in Euclid\u2019s deep fields<\/h2>\n
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\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\n<\/p><\/div>\nHumans and AI classify more than 380 000 galaxies<\/h2>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nGravitational lensing discovery engine<\/h2>\n
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