For two years, an international team studied what astronomers call the Cosmic Dawn – the period in the first few hundred million years after the Big Bang where the first galaxies were born.
Using NASA’s James Webb Space Telescope (JWST), they discovered two of the earliest and most distant galaxies yet confirmed.
Dating back just 300 million years after the Big Bang, these galaxies mark an important milestone in the study of the early universe, according to UC Santa Cruz astronomer Brant Robertson, who leads the JWST Advanced Deep Extragalactic Survey (JADES) team.
“This discovery is completely unexpected and will likely be seen as the most significant extragalactic JWST discovery to date,” said Robertson, a professor of astronomy and astrophysics who is a member of the JADES steering committee. He is the lead author of the first of three papers reporting various aspects of the discovery.
In one paper, the authors conclude: “With populations of high-redshift galaxies established less than 300 million years after the Big Bang, we have extended our reach into the cosmic past by 40% in the first eighteen months of JWST operations.”
“Redshift” refers to an effect caused by the expansion of the universe, where the wavelength of light from distant galaxies is stretched as it travels. In these newly discovered galaxies, the effect is extreme—stretching it by a factor of 15 and shifting even the galaxies’ ultraviolet light to infrared wavelengths where only JWST has the ability to see it.
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Chasing Early Galaxies
Modern theory holds that galaxies develop in special regions where gravity has concentrated cosmic gas and dark matter into dense clumps known as “halos.” These halos evolved rapidly in the early universe, coalescing into increasingly massive collections of matter. This rapid development is why astronomers are so eager to find even earlier galaxies: each small increase moves our gaze to a less evolved period, where the brighter galaxies are even more distinctive and unusual.
“This galaxy is truly a gem and points to more hidden treasures in the early universe,” Professor Robertson said.
Found in a region near Hubble’s Ultradeep Field, the new galaxies, which have been confirmed spectroscopically, are now known as JADES-GS-z14-0 (the more distant one) and JADES-GS-z14-1.
According to NASA, in addition to being the new distance record holder, JADES-GS-z14-0 is remarkable for how big and bright it is. JWST measured the galaxy over 1,600 light-years across. Many of the brightest galaxies produce most of their light through gas falling into a supermassive black hole, producing a quasar. But the team says JADES-GS-z14-0’s large size means the light must be produced by young stars.
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Deeply hidden gems
Still, the massive galaxy was a puzzle to the JADES team when they first spotted it more than a year ago, as it appeared close enough in the sky to a foreground galaxy that they couldn’t be sure the two weren’t neighbors. But in October 2023, the JADES team conducted even more in-depth imaging—five full days with the JWST near-infrared camera of just one field—to form the “JADES Field of Origin.” With the use of filters designed to better isolate early galaxies, confidence has grown that JADES-GS-z14-0 is indeed very far away.
In addition, the galaxy happened to fall into a region where the team had performed ultra-deep imaging with the JWST Mid-InfraRed Instrument. These combined imaging results convinced the team to include the galaxy in what was planned to be the final observation of JADES, a 75-hour campaign to conduct spectroscopy of faint early galaxies. The spectroscopy confirmed their hopes that JADES-GS-z14-0 was indeed a record-breaking galaxy and that a fainter candidate, JADES-GS-z14-1, was almost as far away.
The combination of high brightness and stellar origin makes JADES-GS-z14-0 the most distinctive evidence yet for the rapid formation of large, massive galaxies in the early universe.
“We could detect this galaxy even if it was 10 times fainter, which means we can see other examples even earlier in the universe – probably in the first 200 million years,” Robertson added.
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Robertson Report of May 30, The earliest galaxies in the JADES origin field: The luminosity and density function of the cosmic star formation rate 300 Myr after the Big Bangis accepted for publication in the Astrophysical Journal.
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