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Euclid test images tease of riches to come

Aug 1, 2023

• Euclid’s two instruments have captured their first test images, showcasing space telescope potential to exceed its scientific goals
• These are early test images, taken to check the instruments and review how Euclid can be further tweaked and refined
• The Euclid space mission of the European Space Agency (ESA), launched into space on 1 July 2023, will create the largest and most accurate 3D map of the universe

Caption: First test images of Euclid.
Credits: ESA/Euclid/Euclid Consortium/NASA, CC BY-SA 3.0 IGO.

The Euclid space mission of the European Space Agency (ESA) was launched into space on Saturday, 1 July 2023 to create the largest and most accurate 3D map of the universe. A month later, Euclid’s two instruments have already captured their first test images. The mesmerising results indicate that the space telescope will achieve the scientific goals that it has been designed for—and possibly much more.

Although there are months to go before Euclid delivers its true new view of the cosmos, reaching this milestone means the scientists and engineers behind the mission are confident that the telescope and instruments are working well.

“After more than 11 years of designing and developing Euclid, it’s exhilarating and enormously emotional to see these first images,” says Euclid project manager Giuseppe Racca. “It’s even more incredible when we think that we see just a few galaxies here, produced with minimum system tuning. The fully calibrated Euclid will ultimately observe billions of galaxies to create the biggest ever 3D map of the sky.”

Yannick Mellier, Euclid Consortium lead, adds: “The outstanding first images obtained using Euclid’s visible and near-infrared instruments open a new era to observational cosmology and statistical astronomy. They mark the beginning of the quest for the very nature of dark energy, to be undertaken by the Euclid Consortium.”

The Universe in infrared light

Euclid’s Near-Infrared Spectrometer and Photometer (NISP) instrument has a double role: imaging galaxies in infrared light and measuring the amount of light that galaxies emit at various wavelengths. This second role lets us directly work out how far away each galaxy is.

By combining distance information with that on galaxy shapes measured by the visible instrument VIS (see below), we will be able to map how galaxies are distributed throughout the Universe, and how this distribution changes over time. Ultimately, this 3D map will teach us about dark matter (which causes gravity) and dark energy (which causes the Universe to expand).

Researchers from the Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) at the Institute of Space Sciences (ICE-CSIC), together with the Institute of High Energy Physics (IFAE), have been involved since 2006 in the initial concepts of the mission and have been responsible for the design, construction, assembly and validation tests of the Filter Wheel Assembly (FWA) of the NISP instrument. The Polytechnic University of Cartagena (UPCT), in collaboration with the Instituto de Astrofísica de Canarias (IAC), has been responsible for the design, construction and validation of the control electronics of the NISP Instrument.

Francisco Castander, IEEC researcher at the ICE-CSIC, says: “Each day, we have great expectations to learn the results of Euclid commissioning. So far, we are delighted to see the results that indicate that Euclid is performing as expected. Looking at the spectacular images, we have a gratifying and awesome experience realising that we have built part of the instrument that is collecting those incredible images from far away in space and that will allow us to study the mysteries of the universe.”

In the image below, before reaching the NISP detector the light from Euclid’s telescope has passed through a filter that measures the brightness at a specific infrared wavelength.

Caption: Early commissioning test image – NISP instrument full field of view and zoom in for detail. The image on the left shows the full NISP field of view, with the zoom-in on the right (4% of NISP’s full field of view) demonstrating the extraordinary level of detail that NISP is already achieving. We see spiral and elliptical galaxies, nearby and distant stars, star clusters, and much more. But the area of sky that it covers is actually only about a quarter of the width and height of the full Moon. Euclid’s telescope collected light for 100 seconds to enable NISP to create this image.
Credits: ESA/Euclid/Euclid Consortium/NASA, CC BY-SA 3.0 IGO.

In this second image, the light from Euclid’s telescope had passed through a ‘grism’ before it reached the detector. This device splits light from every star and galaxy by wavelength, so each vertical streak of light in the image is one star or galaxy. This special way of looking at the Universe allows us to determine what each galaxy is made of, which allows us to evaluate its distance from Earth.

Caption: Early commissioning test image – NISP instrument (grism mode). Before it reaches the detector, NISP sends incoming light through either a photometry filter or a spectrometry grism. In this image, the light from Euclid’s telescope has passed through the grism, which splits light from every star and galaxy by wavelength. This information can be pulled out and analysed to determine the type of galaxy and what its distance is. Euclid’s telescope collected light for 100 seconds to enable NISP to create this image.
Credits: ESA/Euclid/Euclid Consortium/NASA, CC BY-SA 3.0 IGO.

NISP instrument scientist Knud Jahnke says: “We’ve seen simulated images, we’ve seen laboratory test images – it’s still hard for me to grasp that these images are now the real Universe. So detailed, just amazing.”

The Universe in visible light

Euclid’s VISible instrument (VIS) will take super sharp images of billions of galaxies to measure their shapes. Looking closely at this image, we already get a glimpse of the bounty that VIS will bring; whilst a few galaxies are very easy to spot, many more are fuzzy blobs hidden amongst the stars, waiting to be unveiled by Euclid in the future.

Caption: Early commissioning test image – VIS instrument full field of view and zoom in for detail. The image on the left shows the full VIS field of view, with the zoom-in on the right demonstrating the extraordinary level of detail that VIS is already achieving. We see spiral and elliptical galaxies, nearby and distant stars, star clusters, and much more. But the area of sky that this zoom-in covers is actually only about a quarter of the width and height of the full Moon. Euclid’s telescope collected light for 566 seconds to create this image.
Credits: ESA/Euclid/Euclid Consortium/NASA, CC BY-SA 3.0 IGO.

Mark Cropper from University College London led the development of VIS: “I’m thrilled by the beauty of these images and the abundance of information contained within them. I’m so proud of what the VIS team has achieved and grateful to all of those who have enabled this capability. VIS images will be available for all to use, whether for scientific or other purposes. They will belong to everybody.”

Reiko Nakajima, VIS instrument scientist adds: “Ground-based tests do not give you images of galaxies or stellar clusters, but here they all are in this one field. It is beautiful to look at, and a joy to do so with the people we’ve worked together with for so long.”

The image is even more special considering that the Euclid team was given a scare when they first switched the instrument on: they picked up an unexpected pattern of light contaminating the images. Follow-up investigations indicated that some sunlight was creeping into the spacecraft, probably through a tiny gap; by turning Euclid the team realised that this light is only detected at specific orientations, so by avoiding certain angles VIS will be able to fulfil its mission.This image was taken at an orientation where the sunlight was not an issue.

It is worth noting once more that these snapshots—beautiful though they are—are still early test images, taken to check the instruments and review how the spacecraft can be further tweaked and refined. Because they are largely unprocessed, some unwanted artefacts remain – for example the cosmic rays that shoot straight across, seen especially in the VIS image. The Euclid Consortium will ultimately turn the longer-exposed survey observations into science-ready images that are artefact-free, more detailed, and razor sharp.

Over the next few months, ESA and industry colleagues will continue to carry out all the tests and checks needed to ensure that Euclid is working as well as possible. At the end of this ‘commissioning and performing verification phase’, the real science begins. At that point ESA will release a new set of images to demonstrate what the mission is capable of.

About the IEEC

The Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) promotes and coordinates space research and technology development in Catalonia for the benefit of society. IEEC fosters collaborations both locally and worldwide and is an efficient agent of knowledge, innovation and technology transfer. As a result of more than 25 years of high-quality research, done in collaboration with major international organisations, IEEC ranks among the best international research centres, focusing on areas such as: astrophysics, cosmology, planetary science, and Earth Observation. IEEC’s engineering division develops instrumentation for ground- and space-based projects, and has extensive experience in working with private or public organisations from the aerospace and other innovation sectors.

The IEEC is a non-profit public sector foundation that was established in February 1996. It has a Board of Trustees composed of the Generalitat de Catalunya, Universitat de Barcelona (UB), Universitat Autònoma de Barcelona (UAB), Universitat Politècnica de Catalunya · BarcelonaTech (UPC), and the Spanish Research Council (CSIC). The IEEC is also a CERCA centre.

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