After the successful launch and commissioning of ESA’s Euclid satellite last summer, today marks the publication of six key papers presenting in detail the mission together with ten papers demonstrating the range of science questions Euclid will address based on observations taken during commissioning. Of the six key papers, IAP scientist and Euclid Consortium Lead Yannick Mellier heads up the Euclid overview paper. IAP scientists and engineers also contributed to the VIS instrument paper, providing the first deep image of the Universe as seen by Euclid’s VIS camera during commissioning. IAP scientist Hakim Atek led the Early Release Observations program on the massive galaxy clusters Abell 2390 and 2764, which demonstrated the immense potential of Euclid to map structures in the Universe using gravitational lensing. These papers, together with the associated datasets from the commissioning observations, are made publicly available today and mark the beginning of the immense scientific return expected from Euclid.

Figure 1Figure 1: A close-up image of the A2390 cluster, released as part of the Early Release Observations program “Magnifying Lens” (PI: H. Atek), highlights the intra-cluster light emitted by free-floating stars that have been ejected from their host galaxies. To enhance visibility, the emission has been accentuated relative to the cluster galaxies. This diffuse emission is thought to trace the spatial distribution of dark matter in the cluster and the cosmic web filaments.
Credits: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre (CEA Paris-Saclay), G. Anselmi; CC BY-SA 3.0 IGO or ESA Standard Licence.

Imagining Euclid

For over two decades, scientists have sought to understand the nature of the accelerated expansion of the Universe, known as dark energy, and the nature of dark matter, which shapes the Universe on large scales. Light rays passing through the Universe are minutely distorted by the presence of dark matter. The effect is so tiny that many galaxies are needed for it to be detectable, but IAP scientists and others first successfully measured this effect in the early 2000s. It was soon realised that this measurement could provide a powerful probe of the overall nature of the geometry of the Universe itself, providing an independent and potent way to constrain both the nature of dark matter and dark energy. However, making these measurements with ground-based observations plagued by atmospheric distortions is hard. It was clear that a dedicated, space-based observatory would be required to make a definitive measurement. At the same time, galaxy clustering emerged as an independent technique to measure the Universe’s geometry. Euclid, together with VIS (VISible instrument) and the infrared spectrometer NISP (Near Infrared Spectro Photometer), is designed to make a simultaneous measurement of both effects in over a billion galaxies over the entire extragalactic sky, promising new and powerful insights into the cosmological model.

Euclid will bring high-resolution, wide-field imaging and distance measurements over almost the entire extragalactic sky. It will have a transformative impact on all of extragalactic astronomy. The six papers published today present six different aspects of Euclid. Here we highlight the important contribution of the IAP to two of these papers. We also highlight one of the Early Release Observations papers, which demonstrates the immense power of wide-field space-based observations.

IAP and the first Euclid key papers

The Euclid overview paper led by consortium lead Yannick Mellier confirms that the telescope and instruments are performing as expected, with IAP teams helping to demonstrate that the satellite can meet mission requirements.

Figure 2Figure 2: A small section (2.′5 × 2.′0) of VIS images from the Euclid Deep Field taken last August. The left panel shows an unprocessed single exposure with clearly visible cosmic rays. The right panel displays a processed stack covering the same area combining 42 exposures using the OU-VIS pipeline, clearly revealing faint and distant galaxies.
Credits: ESA, Euclid, Euclid Consortium, NASA

The Euclid Visible Camera VIS (Cropper et al.) paper describes the mission's high-resolution 609 Megapixel optical camera, the largest ever flown in space. IAP teams (OU-VIS) have led the development of automated software to process its data; the paper demonstrates the camera's performance with the first deep images of the Universe based on commissioning data. The IAP has been involved in simulating Euclid observations since the beginning of the mission; Patrick Hudelot co-leads the Euclid simulation team and this was described in a previous paper.

The Euclid early release observations

A second group of papers released today highlights Euclid’s scientific potential, covering topics from nearby nebulae to galaxy clusters. A paper led by IAP researcher Hakim Atek demonstrates Euclid's ability to identify distant sources, distant sources and galaxy clusters and reveal the large-scale dark matter and intra-cluster light in clusters of galaxies and study early massive galaxies, showcasing its large field of view and impact on understanding the universe's early structures.

These papers, and the associated datasets, are available now through the consortium website and will be posted on arXiv this Friday.

The Euclid team at IAP

Yannick Mellier, Tancrède Ménard, Simon Berquez, Emily Diomat (ECL-SO) ; Patrick Hudelot, Sophie Huot (OU-SIM); Clotilde Laigle, Sylvain Mottet, Catherine Grenet, Thomas Flanet, Olivier Hérent, H. J. McCracken, Kane Nguyen-Kim, Frank Soldano (OU-VIS) ; Hakim Atek (PU-Lead), Grégoire Aufort, Emma Aycoberry, Karim Benabed, Valérie de Lapparent, Simon Ding, Florence Durret, Matthew Ho, Tristan Hoellinger, Florent Leclercq, Axel Lapel, Gary Mamon, Ben Wandelt, Rémi Fahed, Guilhem Lavaux, Pierre Guillard, Céline Gouin, Jean-Philippe Beaulieu, Clément Ranc, Brigitte Rocca.


puce The ESA press release, May, 23, 2024

puce The released papers on the Euclid consortium web site

puce The CNRS-INSU press release (in French)


Layout: Jean Mouette

May 2024

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