A stunning deep-infrared image of the universe by the James Webb Space Telescope has revealed 42 new images of lensed galaxies and revealed at unprecedented depth the shape of the lens, which could eventually help us see the first galaxies.
The disclosure of James Webb Space Telescope deep field image, of US President Joe Biden in a special An event at the White House held on July 11, was a closely guarded secret. Teams of astronomers raced to be the first to analyze it, with three new papers posted on the community preprint server within a week of the image’s release.
“Honestly, we were kind of screwed!” Brenda Fry, an astronomer at the University of Arizona’s Steward Observatory and co-author of one of the papers, told Space.com. “Usually we have a warning a year or two in advance, but no one saw [this release] coming at that time.”
Gallery: The first pictures of the James Webb Space TelescopeConnected: How the James Webb Space Telescope works in pictures
The galaxy cluster SMACS J0723.3-7327, known as SMACS J0723 for short, is among a set of galaxy clusters that Webb has imaged for various gravitational lensing surveys. Other than that, Frye said, there was nothing extraordinary about SMACS J0723 — until now.
“It was beautifully chosen [to be one of the first images] because it was a relatively unknown target,” she said.
Gravitational lenses is a phenomenon in which the gravity of a very massive object distorts space into a shape analogous to an optical lens, causing light to be distorted by everything behind the lens and increase in brightness. Galaxy clusters are particularly effective lenses because they pack a huge amount of mass (in the case of SMACS J0723, about 100 trillion times the mass of the Sun) into a relatively compact volume about 3 to 5 million light-years in diameter. .
Previous studies of Hubble Space Telescope and pensioners Herschel Space Observatory have found a handful of lensing images of background galaxies in their SMACS J0723 observations. But Webb takes hunting to a whole new level.
Fry’s team, led by graduate student Massimo Pascale at the University of California, Berkeley, discovered 42 new lensed images in the background of the new deep-field image. Gravitational lensing can produce multiple images of the same galaxy, so these 42 images represent 19 separate galaxies. Another team led by Gabriel Caminha of the Max Planck Institute for Astrophysics in Germany counted 27 new lensed images.
Whatever the end result, these lensed images allow scientists to refine the map of matter—both visible and dark — propagates into the SMACS J0723 cluster and in turn models the shape of the lens. One of the new papers, by a team led by Guillaume Mahler of Durham University, concludes that most of the mass is concentrated in the brightest, most massive galaxy in the cluster.
Examples of some of the background lensed galaxies in the Webb image of SMACS J0723. (Image credit: NASA/ESA/CSA/STScI/Pascale et al.)
“Our models not only describe the mass, but we can also use them to describe the magnification of these lensed images,” Pascale told Space.com.
The current most distant confirmed galaxy is a distant object known as GN-z11which has a redshift of 11.09, meaning we see it as it existed 13.4 billion years ago, just 400 million years after Big bang. (“Redshift” refers to the stretching of the wavelength of light that occurs as the universe expands between a distant object and the viewer. The higher the redshift factor, the more distant the light source.)
An even more distant candidate is HD1, discovered at a redshift of 13, appears to us as it was only 300 million years after the Big Bang. Even recently, early results from Webb have identified another candidate galaxy at redshift 13 called GLASS-z11. However, astronomers have not yet confirmed the redshift of either HD1 or GLASS-z11.
Webb is expected to break both of these redshift records, although it is not yet known whether any of the lensing galaxies observed in SMACS J0723 are more distant than Gn-z11 or HD1. Pascal and Fry are interested in mapping a phenomenon called the “critical curve” because it is along these curves that gravitational lensing exerts the greatest magnifying power and where astronomers have the best chance of seeing the earliest galaxies.
“The typical magnification in a lensing cluster is about a factor of 10, and that’s not enough to see the first galaxies,” Fry said. “But if we look near the critical curve, that’s where things scale up hundreds or even thousands of times.”
Think of a critical curve as contour lines on a topographic map of the surface of The Earth. The more such contour lines are collected together, the greater the height of any particular spot on the surface. Similarly, a critical curve is where the contour lines of the gravitational potential meet, and the more clustered they are, the stronger that potential and its accompanying increase. The location and shape of the lens images can give an indication of where the critical curve is.
Examples of some of the background lensed galaxies in the Webb image of SMACS J0723. (Image credit: NASA/ESA/CSA/STScI/Pascale et al.)
“Ultimately, what we want to do is look right along the critical curve where the magnification is the largest, and that’s where we’ll find the galaxies with the largest redshift,” Fry said.
That is why the initial trio of new Webb Deep Field papers concentrated on modeling the amount and distribution of matter in the foreground cluster, and therefore the shape of the lens and the location of the critical curve.
However, the modeling can also tell us about the galaxy cluster’s own history.
“We found that the mass distribution was a little more elongated than expected,” Pascale said. “Maybe that says something about cluster merger historyand we can extrapolate from that and learn something about cluster formation in general, which happens in a very chaotic environment where gravity all these galaxies are pulling at each other.”
The immediate next step for Pascal and Fry’s team and the authors of the other two papers is to go through the peer review process to see these results published in scientific journals. Additionally, data from Webb’s Near Infrared Imager and Slitless Spectrograph (NIRISS) awaits analysis and should help scientists determine the spectroscopic redshifts of lensed galaxies and see how far away they are. (The deep-field image was taken by NIRCam, the near-infrared camera.)
“Before Webb imaged it, SMACS J0723 was not the star of the show,” Pascale said. “Now all of a sudden there’s paper after paper on it, which really speaks to how powerful Webb is to reveal things we couldn’t see before.”
The preprint of Pascale and Fry’s article can be found here here. The other two documents are available here and here.
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