Euclid's First Data Release: A Stepping Stone to its 3D Map of the Sky

The ESA's Euclid has already teased us with some early results. In the past it's given us a small, 60 square degree of the sky created with a few days of observations. Those images showed individual targets from the Horsehead Nebula to the Perseus cluster of galaxies. But now we have data from more than one year of the telescope's observations, named DR1-Foundation. DR-1 Foundation covers a sky area as large as about 9,500 full moons, and captures light from more than one billion objects. It took about 13 months to gather all this data. Understanding dark energy and dark matter means studying as much of the Universe as possible. The effects of dark energy and dark matter are felt at large scales, and by constructing an image of galaxy superclusters and the filaments they exist on, as well as the voids between those filaments, Euclid will lead to new understandings of both dark energy and dark matter. There are other efforts to map this structure, some dating back decades. DESI, the Dark Energy Survey Instrument, has created the largest 3D map so far, but Euclid's will be larger. Euclid's will have more depth and volume, and since it's space-based while DESI is ground-based, it won't have to deal with atmospheric interference and will have a higher resolution. This data release is from the Euclid's Wide and Deep Surveys, two surveys that will form the backbone of its 3D map. Even though the data covers 1900 square degrees of the sky, they only represent about 14% of the sky the space telescope will cover in its six-year mission. This image shows Euclid's Wide Survey in light yellow and its Deep Survey in darker yellow. The Deep Survey are targeted regions within the Wide Survey. They're overlain on a star map from Gaia and a dust map from Planck. Image Credit: ESA/Euclid/Euclid Consortium/NASA; ESA/Gaia/DPAC; ESA/Planck Collaboration. Licence: CC BY-SA 3.0 IGO or ESA Standard Licence The Wide Survey is Euclid's primary campaign and will cover almost half of the galactic sky. It's an imaging and spectrographic survey in visible and near-infrared. It's the telescope's main cosmology survey and will cover a large volume to constrain dark energy and dark matter. The Deep Survey serves a different purpose. It'll find fainter objects like dwarf galaxies, low-mass galaxies, and tidal tails, as well as high redshift galaxies and quasars. It will serve to calibrate the Wide Survey, and will provide its own, separate science based on its higher density of sources. Basically, the Wide Durvey provides the greater volume, and the Deep Survey looks more closely and gives more depth. The two combined are needed for a cosmological survey. Part of the release includes Euclid's image of the core of the Messier 81 galaxy group. This image shows part of that, centered on the Messier 81 galaxy, the group's largest member. The smaller NGC 3077 is on the left, which is also a member, as are many other small members spread across the image. Wispy blue clouds, sometimes called 'galactic cirrus clouds' are also visible. An irregular dwarf galaxy is also visible in diffuse blue to the left. Image Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre and E. Bertin. Licence: CC BY-SA 3.0 IGO or ESA Standard Licence Euclid also delivered an image of NGC 1291, a stunning ring galaxy about 33 million light years away. It's also called the Golden Eye galaxy, and it has an inner ring and an outer ring, as well as an inner bar. It's inner and outer rings may be because of a merger with a gas-rich galaxy in the past. This is Euclid's image of NGC 1291, a ring galaxy that faces us head-on. It's about 33 million light years away, and highlights Euclid's power. Image Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre and E. Bertin. Licence: CC BY-SA 3.0 IGO or ESA Standard Licence Euclid also captured images of Abell 3128. It's 800 million light years away and contains hundreds of individual galaxies. Massive clusters like this one are important probes for dark energy and dark matter, but especially for dark matter. They serve as important gravitational lenses and reveal a lot about where dark matter is concentrated. They can help cosmologists test Lambda-Cold Dark Matter, which is the standard Big Bang theory of the Universe. They also help Euclid calibrate itself. This is the Abell 3128 cluster, part of the Horologium supercluster. Horologium is home to more than 30 smaller clusters, and Abell 3128 is one of its richest members. Abell holds spirals and ellipticals, and a gravitational lens is in the middle, warping and magnifying the light from a distant background galaxy. The image shows only a fraction of Abell 3128, and also part of another galaxy cluster named ACT-CL J0330-5227; while in reality the two clusters are separated by a huge distance of around 5 billion light-years, they overlap here in our line of sight. Image Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre and E. Bertin. Licence: CC BY-SA 3.0 IGO or ESA Standard Licence We're only at the appetizer of the visual and scientific feast that Euclid will deliver. By the time it's completed, its 3D map of the sky will be visually entrancing and full of science. It's already discovered a new comet, the most ancient quasar in the Universe, and new images of the Milky Way's over-populated center. It's off to a strong start and will only get better. You can explore previous images from Euclid's 2024 Early Release Observations (ERO) and its Quick Euclid data release 1 (Q1) from 2025 at ESA Sky.