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Webb reveals new details in Pandora’s Cluster

Astronomers have captured a new deep field of Pandora's Cluster (Abell 2744) with the James Webb Space Telescope. The images show never-before-seen details. The results are described in four scientific papers. Leiden astronomers Marijn Franx and Mariska Kriek collaborated on the study. 'This opens a new perspective on the evolution of galaxies.'

Webb image of Pandora's Cluster showing an estimated 50,000 sources of near-infrared light.

The new Webb image shows three clusters of massive galaxies forming a mega-cluster together. The combined mass of the clusters creates a powerful gravitational lens, a natural magnification effect of gravity. This allows astronomers to observe much more distant galaxies in the early universe. Pandora's Cluster lies in the southern constellation Sculptor, 3.5 billion light years from Earth. The new image of Pandora's Cluster merges four Webb pictures into one panoramic image and shows roughly 50,000 sources in near-infrared light.

Only Pandora's central core has previously been studied in detail by the Hubble Space Telescope. By combining Webb's infrared instruments, with a broad mosaic image of the different lensing regions in the area, the astronomers arrived at this wide and deep field. According to Mariska Kriek, this 'opened a new window to the study of cosmology and the evolution of galaxies.'

Webb exceeds expectations

'When the Webb images of Pandora's Cluster came in, we were a bit overwhelmed,' says astronomer Rachel Bezanson. She is co-principal investigator of the Webb programme that did this research, named 'Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionisation' (UNCOVER). 'There were so many details in the foreground cluster and so many distant, lensed galaxies, that I got lost in the image. Webb exceeded our expectations.'

Apart from magnification, the gravitational lens distorts the appearance of distant galaxies in a way that they look very different from those in the foreground. The lens effect of the cluster is so strong that it distorts the fabric of space itself. As a result, light from distant galaxies travelling through that distorted space, also looks distorted.

Take a Tour of Pandora's Cluster

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Hundreds of distant lens-shaped galaxies to be seen

Fellow principal investigator Ivo Labbé Swinburne, points to the area in the lower right corner of the Webb image. That part never has been captured by Hubble. 'There, hundreds of distant lens-shaped galaxies can be seen, appearing as faint arc lines. Zooming in on the area, more and more become visible. My first reaction to the image was that it is so beautiful, it looks like a simulation of galaxy formation. We had to remind ourselves that these were real observations, and that we are now working in a new era of astronomy.'

Team member Pratika Dayal added: 'These rich datasets can also help us shed new light on the nature of dark matter in the era of the history of the universe that is not accessible in any other way.'

Near-Infrared Camera observations

The UNCOVER team used Webb's Near-Infrared Camera (NIRCam) to capture the cluster with exposures between 4-6 hours. They had a total of about 30 hours observing time. The next step is to meticulously review the data from the images and select galaxies for follow-up observations with the NIRSpec. These will provide accurate distance measurements, along with other detailed information on the composition of the lensed galaxies. It will provide new insights into the early era of galaxy formation and evolution. The UNCOVER team expects Webb to make these NIRSpec observations in the summer of 2023.

In the meantime, all photometric data from NIRCam has been made public so other astronomers can become familiar with it. This way, they can plan their own scientific studies with Webb's rich datasets. 'We want to help the astronomy community to take full advantage of the fantastic machine that Webb is,' says Leiden astronomer Marijn Franx. 'This is just the beginning of all the amazing Webb science to come.'

Scientific articles

 • The JWST UNCOVER Treasury survey: Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization
Bezanson, R.; Labbe, I.; Whitaker, K. E.; et al.; 2022, arXiv:2212.04026
 • UNCOVERing the extended strong lensing structures of Abell 2744 with the deepest JWST imaging
Furtak, L. J.; Zitrin, A.; Weaver, J. R.; et al.; 2022, arXiv:2212.04381
 • JWST UNCOVER: A triply imaged extremely red and compact object at zphot≃7.7
Furtak, L. J.; Zitrin, A.; Plat A.; et al.; 2022, arXiv:2212.10531
• The UNCOVER Survey: A first-look HST+JWST catalog of 50,000 galaxies near Abell 2744 and beyond
Weaver, J. R.; Cutler, S. E.; Pan, R.; et al.; 2023, arXiv:2301.02671

This article was published as a press release on the website of NOVA.
Picture: NASA, ESA, CSA, Ivo Labbe,  Rachel Bezanson; image processing: Alyssa Pagan (STScI)

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