The JWST’s first deep field may have broken the record for the most distant known galaxy for the third time — possibly. Image credit: NASA, ESA, CSA and STScI
One of the main functions of JWST is to search for the earliest galaxies, expanding our space-time exploration of the universe. In the weeks since the space telescope first released its data, astronomers have mined its output to reveal a galaxy that is older than any we’ve ever discovered before, before possibly breaking that record again. The title of oldest and most distant galaxy may have been broken for the third time, but in this case, what is known as a “Schrödinger’s candidate galaxy” is less clear.
A preprint of a paper that has not yet been peer-reviewed considers the case of CEERS-1749. On the one hand, we see this galaxy about 220 million years after the Big Bang. If so, it would not only easily break the record for the most distant galaxies, but it would refute nearly all discovered models of early galaxy evolution. Such evolved galaxies should not have formed so quickly. On the other hand, it is unusual for some other measure to bring CEERS-1749 so close to us in a completely different way.
When exploring the early universe, the most important measurement is z, or redshift. This measures the speed at which objects are moving away from us, causing spectral lines to move toward the lower end of the spectrum, like a siren sounding deeper as it passes us. The expansion of the universe means that the more redshift a galaxy or star is, the further away it may be and the earlier we see it.
Before this year, the record for the highest redshift galaxy we saw was z=11. Shortly after the first JWST release, a team led by Dr. Rohan Naidu of Harvard University and the Smithsonian Center for Astrophysics reported z=13 galaxies and subsequently topped the list of z=14 candidates. Meanwhile, a recent paper exploring the most distant galaxies sufficient to measure their metallicity deals with values around 8.
So if CERES-1749’s 0.6 – 5µm photometric measurements are correct with a redshift of z≈17, then this is indeed a very significant breakthrough. CEERS-1749, on the other hand, has three distinct neighbors, z≈5 (12.5 billion years). It is possible that it is actually part of a cluster of this group, and the apparent redshift of more than three times is an illusion. It’s this uncertainty that led Naidu and co-authors to label CERES-1749 a “Schrödinger candidate,” which is currently both the oldest known galaxy and billions of years younger.
Even though CEERS-1749 is part of a z=5 cluster, it may still set different records. To observe it at a distance of z=5, it would have to be either a galaxy where star formation started and then largely stopped, or a smaller galaxy with unusually thick dust (another team’s preprint also suggested small and dusty scene). In these cases; “It would be either the highest redshift quiescent galaxy, or one of the lowest mass dusty galaxies in the early Universe discovered to date,” Naidu and co-authors wrote. Both will challenge existing models of galactic evolution, if not so profoundly.
This could be the second possibility that led to Naidu’s cryptic tweet:
Nine days later, he shared preprint. Astronomy as a field may never have developed as rapidly as it has in recent weeks.
If galaxies with a redshift of 5 were mimicking something much older, that would pose a considerable challenge to cosmologists.However, the authors concluded: “This fully camouflaged contaminant is only possible within a narrow redshift window (Δz < 0.1)." A co-author Comment It also requires a specific combination of telescope filters, so it’s unlikely to be a factor we often worry about.
“Spectral tracking of this extraordinary galaxy is critical to JWST’s mission to expand the boundaries of the universe… If this source is indeed located at z ≈ 17, we may embark on the grand endeavor of modifying the physics of galaxy evolution at the earliest times,” the authors write . Unfortunately, the world’s most precious telescope time doesn’t come easily.