Euclid finds thousands of new galaxies

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This image is a small section of a larger image taken by Euclid showing the gala
This image is a small section of a larger image taken by Euclid showing the galaxy cluster Abell 2390. Many features caused by gravitational lensing can be seen, including the huge arc of a distant red galaxy. 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 License.
Launched last year, ESA’s Euclid space telescope has already been delivering data for almost a year. The first scientific results are being published today. They show that the new instrument is capable of detecting a representative sample of all galaxies in the universe. For example, a study led by the University of Innsbruck was able to identify over 600 previously unknown dwarf galaxies in the Perseus galaxy cluster.

The study led by Francine Marleau from the Institute of Astro- and Particle Physics at the University of Innsbruck has identified a total of 1100 dwarf galaxies in the Perseus galaxy cluster, 630 of which were previously undiscovered. Dwarf galaxies are very difficult to find because they are not very bright and their light is diffuse across the sky. The team led by Francine Marleau analyzed the structure and size of the dwarf galaxies based on data from the Euclid space telescope and also found clusters of stars around the galaxies. With the help of the discovered galaxies, the team was also able to determine the so-called luminosity function. "This function can be understood as the result of a census," explains Francine Marleau. "It indicates how many galaxies there are with a certain luminosity. With the newly discovered dwarf galaxies, we were able to extend our knowledge of this function to much dimmer galaxies."

In addition to the Perseus galaxy cluster, the nine scientific papers that have now been published also examined the Fornax galaxy cluster, where 5,000 new star clusters were found. "In addition, galaxies were discovered in our ’closer’ neighborhood," says Laila Linke, postdoctoral researcher at the Institute of Astro- and Particle Physics and project leader. "In astronomical terms, however, close still means 1.6 to 29.7 million light years away from Earth." There, the telescope can take images of individual stars and the scientists can use them to characterize different stellar populations.

On the trail of dark matter

Clusters of galaxies contain a lot of dark matter. Their mass distorts the observed shapes of distant background galaxies due to the gravitational lensing effect. Research group leader Tim Schrabback, also at the Institute of Astro- and Particle Physics, analyzed the dark matter of the galaxy cluster Abell 2390 with an international team. "Our study shows how excellently suited the new instrument is for this analysis," says Tim Schrabback. By distorting the shapes of background galaxies, we were able to measure the distribution of dark matter in and around the galaxy cluster.

The new results demonstrate the strengths of the Euclid telescope: "The new instrument can observe a large area of the night sky at once and therefore provides a representative sample of all galaxies," says Laila Linke. "Thanks to the high sensitivity to surface brightness, we can also find dwarf galaxies and very diffuse galaxies. With the particularly sharp images thanks to the high spatial resolution, we can identify dwarf galaxies and at the same time discover and characterize so-called nuclear star clusters and globular clusters."

New instrument for science

The European Space Agency’s (ESA) Euclid space telescope was launched almost a year ago, on July 1, 2023, and is set to create the largest 3D map of the universe to date. Scientists hope to learn more about the previously unexplored dark matter and dark energy in the universe. The data from Euclid will be analyzed by the international Euclid consortium. Over the next few years, the space telescope with a diameter of 1.2 meters will create the largest and most accurate 3D map of the universe and observe billions of galaxies. Euclid can use this map to reveal how the universe expanded after the Big Bang and how the structures in the universe have developed. This will give scientists more clues to better understand the role of gravity and the nature of dark energy and dark matter. The Euclid consortium - consisting of 2,000 scientists at 300 research institutions in 15 countries - is analyzing the mission data. The data is also supplemented with earthbound telescopes. The research teams of Tim Schrabback and Francine Marleau at the University of Innsbruck are significantly involved in the project.

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