The seven galaxies highlighted in this new image from the NASA/ESA/CSA James Webb Space Telescope have been confirmed to be at a distance that astronomers refer to as redshift 7.9, which correlates to 650 million years after the Big Bang. This makes them the earliest galaxies yet to be spectroscopically confirmed as part of a developing galaxy cluster.
This Webb image shows member galaxies of the galaxy cluster A2744-z7p9OD. Image credit: NASA / ESA / CSA / T. Morishita, IPAC / A. Pagan, STScI.
Galaxy clusters are the greatest concentrations of mass in the known Universe, which can dramatically warp the fabric of spacetime itself.
This warping, called gravitational lensing, can have a magnifying effect for objects beyond the cluster, allowing astronomers to look through the cluster like a giant magnifying glass.
Dr. Takahiro Morishita, an astronomer at the IPAC-California Institute of Technology, and colleagues were able to utilize this effect, looking through Pandora’s Cluster (Abell 2744) to view a protocluster in the early Universe.
“This is a very special, unique site of accelerated galaxy evolution, and Webb gave us the unprecedented ability to measure the velocities of these seven galaxies and confidently confirm that they are bound together in a protocluster,” Dr. Morishita said.
“The precise measurements captured by Webb’s Near-Infrared Spectrograph (NIRSpec) were key to confirming the galaxies’ collective distance and the high velocities at which they are moving within a halo of dark matter — more than about 1,000 km per second (2 million mph).”
The NIRSpec spectral data allowed the astronomers to model and map the future development of the gathering group, all the way to our time in the modern Universe.
The prediction that the protocluster, named A2744-z7p9OD, will eventually resemble the Coma Cluster means that it could eventually be among the densest known galaxy collections, with thousands of members.
“We can see these distant galaxies like small drops of water in different rivers, and we can see that eventually they will all become part of one big, mighty river,” said Dr. Benedetta Vulcani, an astronomer at Italy’s National Institute of Astrophysics.
Exploring how large clusters like Pandora and Coma first came together has been difficult, due to the expansion of the Universe stretching light beyond visible wavelengths into the infrared, where astronomers lacked high-resolution data before Webb.
Webb’s infrared instruments were developed specifically to fill in these gaps at the beginning of the Universe’s story.
The seven galaxies confirmed by Webb were first established as candidates for observation using data from Hubble’s Frontier Fields program.
The program dedicated Hubble time to observations using gravitational lensing, to observe very distant galaxies in detail.
However, because Hubble cannot detect light beyond near-infrared, there is only so much detail it can see.
Webb picked up the investigation, focusing on the galaxies scouted by Hubble and gathering detailed spectroscopic data in addition to imagery.
“It is amazing the science we can now dream of doing, now that we have Webb,” said Dr. Tommaso Treu, an astronomer at the University of California, Los Angeles.
“With this small protocluster of seven galaxies, at this great distance, we had a one hundred percent spectroscopic confirmation rate, demonstrating the future potential for mapping dark matter and filling in the timeline of the Universe’s early development.”
The discovery is reported in a paper in the Astrophysical Journal Letters.
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Takahiro Morishita et al. 2023. Early Results from GLASS-JWST. XIV. A Spectroscopically Confirmed Protocluster 650 Million Years after the Big Bang. ApJL 947, L24; doi: 10.3847/2041-8213/acb99e
