In 2024, the James Webb Space Telescope discovered the most distant galaxy ever detected, named JADES-GS-z14-0. JADES stands for JWST Advanced Deep Extragalactic Survey, an observing program that uses the JWST’s groundbreaking observing power to study galaxies at extremely high redshifts. This area of study is one of the telescope’s main science goals.
At redshift z=14.32, the light from JADES-GS-z14-0 has been travelling for almost the entire age of the Universe. That redshift corresponds to a time about 13.5 billion years ago when the Universe was only 2% of the age it is now.
In new research published in Nature Astronomy, a large team of researchers, including some original discoverers of JADES-GS-z14-0, examined the galaxy again. The research is “Photometric detection at 7.7 μm of a galaxy beyond redshift 14 with JWST/MIRI.” The lead author is Jakob Helton from the Steward Observatory at the University of Arizona.
JADES-GS-z14-0 is not only extremely distant, it’s also a very bright galaxy for one so young. Astronomers expected that galaxies in the very early Universe would be smaller and dimmer. According to models, there hadn’t been enough time for galaxies to grow massive and bright. The brightness indicates lots of active star formation, and the discovery led to questions about how such a young, primordial galaxy could be so large and bright.
“We’re able to understand galaxies that are well beyond anything humans have ever found and see them in many different ways and really understand them.” – study co-author Kevin Hainline, University of Arizona, Steward Observatory.
The research shows that it contains half a billion solar masses, a startling number for such a young galaxy. The authors write that it likely experienced a “strong burst of star formation in the most recent few million years.” So, in the galaxy’s recent past, it underwent a period of intense star birth.
“It’s not just a tiny little nugget. It’s bright and fairly extended for the age of the universe when we observed it,” said study co-author Kevin Hainline, an associate research professor at the U of A Steward Observatory.
However, it’s not just its brightness that garnered interest. The galaxy has a high metallicity for one so young.
The JWST’s MIRI instrument played a big role in these findings. MIRI detected the galaxy photometrically at 7.7 μm. This is significant because, at this wavelength, the JWST is detecting light emitted in the rest-frame optical part of the spectrum for a galaxy at this high redshift. Rest frame refers to what the light would look like if it wasn’t red-shifted by the expansion of the Universe. Seeing in the “rest-frame optical part of the spectrum” means MIRI can see atoms like oxygen, whose emission lines are in the optical part of the spectrum.
“While weak rest-frame ultraviolet emission lines have only been seen in a handful of sources, the stronger rest-frame optical emission lines are highly diagnostic and accessible at mid-infrared wavelengths with the Mid-Infrared Instrument (MIRI) of JWST,” the authors write, summing it up. They also write that “at least one-third of the flux at 7.7 μm originates from the rest-frame optical emission lines Hβ and/or [O iii].” Hβ, or hydrogen beta, is one of hydrogen’s emission lines. The really interesting part is the O iii oxygen emission line.
In astronomy, oxygen is a metal. Any atom heavier than hydrogen or helium is called a metal. The Big Bang created only hydrogen and helium, and everything heavier than them was made in stars via nucleosynthesis. This means that somehow, enough stars had already lived and exploded as supernovae in JADES-GS-z14-0 to increase its metallicity, something unexpected in such a young galaxy.
“The inferred properties of JADES-GS-z14-0 suggest rapid mass assembly and metal enrichment during the earliest phases of galaxy formation,” the authors write. The galaxy could’ve already been forming stars for 100 million years before it was observed.
Alternative explanations exist, but according to the authors, they’re not very likely. These results push back star formation to a much earlier time than thought, and they also push back the time when the first galaxies must have assembled.
“The detection of JADES-GS-z14-0 at z > 14 by MIRI demonstrates its power in understanding the properties of the earliest galaxies,” the authors write. The study used 43 hours of MIRI imaging time and 167 hours of NIRCam imaging. Overall, it took nine days of JWST observing time.
The JADES program focuses on two tiny areas of the sky: the Hubble Deep Field (GOODS-N) and Hubble Ultra Deep Field (GOODS-S). There’s a bit of serendipity involved in detecting JADES-GS-z14-0. If they had pointed the telescope even a fraction of one degree differently, they would’ve missed it.
This image taken by the James Webb Space Telescope highlights the region of study by the JWST Advanced Deep Extragalactic Survey (JADES), which is in and around the Hubble Space Telescope’s Ultra Deep Field. Image credit: NASA, ESA, CSA, and M. Zamani (ESA/Webb). Science: B. Robertson (UCSC), S. Tacchella (Cambridge), E. Curtis-Lake (Hertfordshire), S. Carniani (Scuola Normale Superiore), and the JADES Collaboration.
“Imagine a grain of sand at the end of your arm. You see how large it is on the sky – that’s how large we looked at,” said lead author Helton, a graduate researcher at Steward Observatory.
“The fact that we found this galaxy in a tiny region of the sky means that there should be more of these out there,” said Helton. “If we looked at the whole sky, which we can’t do with JWST, we would eventually find more of these extreme objects.”
Leading up to the launch of the JWST, astronomers knew it would generate some surprising results that tested and challenged their models. Our models of the Universe are limited by what data and observations astronomers can gather, and the JWST has made and continues to make a huge contribution to our observational data of the early Universe. So now, with its results in hand, scientists need to construct new models and generate a new understanding of the early Universe.
