Cosmic Atlas: Euclid's deep insights

Millions of stars and galaxies can be seen on the first section of their detailed mapping of the universe, which has now been published by ESA's Euclid space mission. The captured strip across the sky demonstrates the stunning data quality at all levels, from wide-angle views of the Universe to the details of structures inside individual galaxies. Several German research institutes including LMU are involved in this mission.

The first chunk of the final map contains 260 observations made between March 25 and 8 April 2024. In just two weeks, Euclid covered 132 square degrees of the Southern Sky in pristine detail, more than 500 times the area of the full Moon. “Euclid has turned its keen eye to the sky and is working through its observation programme. Scientists and engineers are happy to be able to reap the rewards of 15 years of preparation,” says physicist Frank Grupp, based at LMU and the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching. He is the German project manager.

This mosaic accounts for 1 per cent of the wide survey that Euclid will capture over six years. During this survey, the telescope observes the shapes, distances and motions of billions of galaxies out to 10 billion light-years. Doing this will create the largest cosmic 3D map ever made.

This first piece of the map already contains some 14 million galaxies that could be used to study the hidden influence of dark matter and dark energy on the Universe. It also contains tens of millions of stars in our own Milky Way. “This stunning image is the first piece of a map that will reveal more than one third of the sky in six years,” says Valeria Pettorino, Euclid Project Scientist at ESA.

The spacecraft’s sensitive cameras captured an incredible number of objects in great detail. Zooming very deep into the mosaic, we can still clearly see the intricate structure of a spiral galaxy.

A special feature visible in the mosaic is dim clouds between the stars in our galaxy; they appear in light blue against the black background of space. They are a mix of gas and dust, also called ‘galactic cirrus’ because they look like cirrus clouds. Euclid can see these clouds with its super sensitive visible light camera because they reflect optical light from the Milky Way. The clouds also shine in far-infrared light, as seen by ESA’s Planck mission.

The mosaic released now is a teaser for what’s to come from the Euclid mission. Since the mission started its routine science observations in February, 12 per cent of the survey has been completed. The resulting images already deliver a glimpse of the challenge for the data collection and processing infrastructure. Never before has an astronomical space mission delivered so much data in such a short time – around 100 gigabyte of images and spectra are sent to Earth every day.

Processing of data as a central task

A central concern of the project is the daily processing of this data. For this purpose, the Euclid consortium has set up a European network of nine data centres, including the German Science Data Center (SDC-DE), which will handle 10 per cent of the data. A team of six scientists and IT specialists develops algorithms and maintains the hardware. “The constantly changing software and hardware presents our team with major challenges to assure the timely processing,” says Maximilian Fabricius (LMU and MPE), head of the SDC-DE. “However, we are proud of how well everything is now coming together and that we are now on track for processing for the first public data release.”

The release of 53 square degrees of the survey, including a preview of the Euclid Deep Field areas, is planned for March 2025. The mission’s first year of cosmology data will be released to the community in 2026.