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Only Pandora's central core has previously been studied in detail by NASA's Hubble Space Telescope. By combining Webb's powerful infrared instruments with a broad mosaic view of the region's multiple areas of lensing, astronomers aimed to achieve a balance of breadth and depth that will open up a new frontier in the study of cosmology and galaxy evolution.
"The ancient myth of Pandora is about human curiosity and discoveries that delineate the past from the future, which I think is a fitting connection to the new realms of the universe Webb is opening up, including this deep-field image of Pandora's Cluster," said astronomer Rachel Bezanson of the University of Pittsburgh in Pennsylvania, co-principal investigator on the "Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization" (UNCOVER) program to study the region.
"When the images of Pandora's Cluster first came in from Webb, we were honestly a little star struck," said Bezanson. "There was so much detail in the foreground cluster and so many distant lensed galaxies, I found myself getting lost in the image. Webb exceeded our expectations." The new view of Pandora's Cluster stitches four Webb snapshots together into one panoramic image, displaying roughly 50,000 sources of near-infrared light.
In addition to magnification, gravitational lensing distorts the appearance of distant galaxies, so they look very different than those in the foreground. The galaxy cluster "lens" is so massive that it warps the fabric of space itself, enough for light from distant galaxies that passes through that warped space to also take on a warped appearance.
Astronomer Ivo Labbe of the Swinburne University of Technology in Melbourne, Australia, co-principal investigator on the UNCOVER program, said that in the lensing core to the lower right in the Webb image, which has never been imaged by Hubble, Webb revealed hundreds of distant lensed galaxies that appear like faint arced lines in the image. Zooming in on the region reveals more and more of them.
"Pandora's Cluster, as imaged by Webb, shows us a stronger, wider, deeper, better lens than we have ever seen before," Labbe said. "My first reaction to the image was that it was so beautiful, it looked like a galaxy formation simulation. We had to remind ourselves that this was real data, and we are working in a new era of astronomy now."
The UNCOVER team used Webb's Near-Infrared Camera (NIRCam) to capture the cluster with exposures lasting 4-6 hours, for a total of about 30 hours of observing time. The next step is to meticulously go through the imaging data and select galaxies for follow-up observation with the Near-Infrared Spectrograph (NIRSpec), which will provide precise distance measurements, along with other detailed information about the lensed galaxies' compositions, providing new insights into the early era of galaxy assembly and evolution. The UNCOVER team expects to make these NIRSpec observations in the summer of 2023.
In the meantime, all of the NIRCam photometric data has been publicly released so that other astronomers can become familiar with it and plan their own scientific studies with Webb's rich datasets. "We are committed to helping the astronomy community make the best use of the fantastic resource we have in Webb," said UNCOVER co-investigator Gabriel Brammer of the Niels Bohr Institute's Cosmic Dawn Center at the University of Copenhagen. "This is just the beginning of all the amazing Webb science to come."
The imaging mosaics and catalog of sources on Pandora's Cluster (Abell 2744) provided by the UNCOVER team combine publicly available Hubble data with Webb photometry from three early observation programs: JWST-GO-2561, JWST-DD-ERS-1324, and JWST-DD-2756.
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