The James Webb Space Telescope’s spectacular image of the deep infrared universe has uncovered 42 new images of lensed galaxies and revealed unprecedented depth to the shape of the lens, which may help us see the earliest galaxies.
The revelation of James Webb Space Telescope deep field image of US President Joe Biden in a special White House event held on July 11, was a well-kept 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 publication.
“We got a bit sidetracked, to be honest!” Brenda Frye, 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 year or two notice, but nobody saw that [this release] coming at this time.”
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The galaxy The cluster SMACS J0723.3-7327, known as SMACS J0723 for short, is among a set of galaxy clusters that Webb is imaging for several gravitational lensing surveys. Beyond that, Frye said, there was nothing exceptional about SMACS J0723, until now.
“He was very chosen [to be one of the first images] because it was a relatively unknown target,” he said.
Gravitational lenses is a phenomenon in which the gravity of a very massive object warps space into a shape analogous to an optical lens, causing the light behind the lens to be distorted and magnified in brightness. Clusters of galaxies are particularly efficient lenses because they pack a large amount of mass (in the case of SMACS J0723, about 100 trillion times the mass of the Sun) into a relatively compact volume with a diameter of between 3 and 5 million light years in diameter. .
Previous surveys of the Hubble Space Telescope and retirees Herschel Space Observatory had found a handful of lensed images of background galaxies in their SMACS J0723 observations. But Webb takes hunting to a whole new level.
Frye’s team, which was led by graduate student Massimo Pascale of the University of California, Berkeley, discovered 42 new images with lenses in the background of the new deep-field image. Gravitational lensing can create multiple images of the same galaxy, so these 42 images represent 19 individual galaxies. Another team, led by Gabriel Caminha of the Max Planck Institute for Astrophysics in Germany, counted 27 new lensed images.
Whatever the final tally, these lensed images allow scientists to fine-tune a map of how matter, both visible and dark — is distributed in 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, concluded that most of the mass is concentrated in the cluster’s brightest and most massive galaxy.
Examples of some of the lensed background 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 the 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 larger the stretching factor redshift, the further away the light source is.)
An even more distant candidate is HD1, discovered at a redshift of 13, appears to us as it did just 300 million years after the Big Bang. Even more recently, Webb’s first results have identified another candidate galaxy at redshift 13, called GLASS-z11. However, astronomers have not yet confirmed the redshifts of HD1 or GLASS-z11.
Webb is expected to beat both of these redshift records, although it has not yet been determined whether any of the lensed galaxies seen in SMACS J0723 are more distant than Gn-z11 or HD1. Pascale and Frye are interested in mapping a phenomenon called the “critical curve,” because it is along these curves that gravitational lensing applies the greatest magnifying power and where astronomers have the best chance of seeing the the first galaxies.
“The typical magnification of a lensing cluster is a factor of 10, and that’s not enough to see the first galaxies,” Frye said. “But if we look close to 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 land. The more these contour lines are grouped together, the higher the height of any particular point on the surface. Similarly, a critical curve is where the contours of the gravitational potential are clustered together, and the more clustered they are, the stronger that potential and the expansion that goes with it. The location and shape of the lens images can give an indication of where the critical curve is.
Examples of some of the lensed background 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 highest, and that’s where we’re going to find the highest redshift galaxies,” Frye said.
Therefore, the initial trio of new Webb Deep Field papers focus on modeling the amount and distribution of matter in the foreground cluster and, consequently, the shape of the lens and the location of the critical curve.
However, the modeling can also tell us the story of the galaxy cluster itself.
“We found that the mass distribution was a bit more elongated than expected,” Pascale said. “Maybe that says something about cluster merge historyand we can extrapolate that and learn something about cluster formation as a whole, which occurs in a very chaotic environment where gravity of all these galaxies are stretched together.”
The immediate next step for Pascale and Frye’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. Beyond that, data from Webb’s Near Infrared Imager and Slitless Spectrograph (NIRISS) is pending analysis and should help scientists determine the spectroscopic redshifts of lensed galaxies and see how far they are (The deep-field image was captured 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, which really speaks to how powerful Webb is, to reveal things we couldn’t see before.”
The preprint of Pascale and Frye’s paper can be found here here. The other two roles are available here i here.
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