For two years now, an international team has been studying what astronomers refer to as the Cosmic Dawn – the period of the first few hundred million years after the Big Bang, when the first galaxies were born.
Using NASA’s James Webb Space Telescope (JWST), they have now discovered two of the oldest and most distant galaxies yet confirmed.
According to University of California, Santa Cruz astronomer Brant Robertson, who co-led the JADES (JWST) team, these galaxies date from just 300 million years after the Big Bang and represent a major milestone in the study of the early universe. Advanced Deep Extragalactic Exploration).
“This discovery is completely unexpected and will likely be considered the most significant extragalactic discovery with JWST to date,” said Robertson, a professor of astronomy and astrophysics who sits on the JADES steering committee. He is the lead author of the first of three papers describing various aspects of the discovery.
In one paper, the authors concluded: “With populations of high-redshift galaxies now 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’s operation.
“Redshift” refers to the effect caused by the expansion of the universe, where the wavelength of light from distant galaxies is stretched as it moves. In these newly discovered galaxies, the effect is extreme—stretching by a factor of 15, moving even the galaxies’ ultraviolet light into infrared wavelengths where only JWST can see it.
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The hunt for 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 haloes rapidly evolve in the early universe and coalesce into increasingly massive collections of matter. This rapid evolution is why astronomers are so eager to find even earlier galaxies: Each small increment moves our eyes to a less evolved period, where the brighter galaxies are even more prominent and unusual.
“This galaxy is truly a gem and points to other hidden treasures in the early universe,” Professor Robertson said.
The new galaxies that have been spectroscopically confirmed, found in the region near the Hubble Ultra Deep Field, are now known as JADES-GS-z14-0 (the more distant one) and JADES-GS-z14-1.
In addition to being the new distance record holder, JADES-GS-z14-0 is remarkable for how big and bright it is, according to NASA. JWST measures a galaxy over 1,600 light-years across. Many of the most luminous galaxies produce most of their light by gas falling into a supermassive black hole, forming 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
And yet the massive galaxy was a puzzle to the JADES team when they first spotted it more than a year ago, because it appears close enough in the sky to the foreground galaxy that they couldn’t be sure the two weren’t neighbors. But in October 2023, the JADES team took an even deeper image—five full days with the JWST Near-Infrared Camera on just one field—to create the “JADES Origins Field.” Using filters designed to better isolate early galaxies, the certainty that JADES-GS-z14-0 is indeed very distant has increased.
Additionally, the galaxy happened to fall into the region where the team was conducting ultra-depth 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 culmination of JADES observations, a 75-hour campaign to perform spectroscopy on faint early galaxies. Spectroscopy confirmed their hope that JADES-GS-z14-0 is indeed the galaxy of record – and that a fainter candidate, JADES-GS-z14-1, is almost as far away.
The combination of high luminosity and stellar origin makes JADES-GS-z14-0 the strongest 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 could see other examples even earlier in the universe – probably within the first 200 million years,” Robertson added.
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Robertson’s letter of May 30, The oldest galaxies in the JADES Origins field: Luminosity function and cosmic star formation rate Density 300 Myr after the big bangis accepted for publication in the Astrophysical Journal.
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