JWST’s first deep field may have broken the record for the most distant known galaxy, possibly for the third time. Image credit: NASA, ESA, CSA and STScI
One of the main functions of the JWST is to find the earliest galaxies, expanding our exploration of the universe in both space and time. In the few weeks since the first release of data from the space telescope, astronomers have mined their output to reveal a galaxy older than any we’ve seen before, and then possibly broke that record again. The title of the oldest and most distant galaxy may have already been broken for the third time, but in this case, the situation – dubbed the “Schrödinger galaxy candidate” – is much less clear.
A preprint of an article that has not yet been peer-reviewed considers the case of CEERS-1749. For one thing, we’re seeing this galaxy as it was about 220 million years after the Big Bang. If so, it would not only comfortably break the record for the most distant galaxy, but would disprove nearly every model of early galaxy evolution ever found. Galaxies that have evolved should not have formed so quickly. On the other hand, some other measurements bring CEERS-1749 so close to us that it would be unusual in a completely different way.
When it comes to exploring the early universe, the most important measurement is z, the redshift. This measures how fast an object is moving away from us, causing the spectral lines to shift towards the lower end of the spectrum, in the same way that sirens sound deeper as they pass us. The expansion of the universe means that the more redshifted a galaxy or star is, the further away it is likely to be, and the further back in time we are seeing it.
Before this year, the record for the highest redshift galaxy we had seen was z=11. Shortly after JWST’s first launch, a team led by Dr. Rohan Naidu of the Harvard-Smithsonian Center for Astrophysics reported the az=13 galaxy, later surpassed by an az=14 candidate. Meanwhile, a recent paper exploring the most distant galaxies visible enough to measure their metal content dealt with values around 8.
Consequently, if the 0.6 – 5 µm photometry measurement of CERES-1749 as having a redshift of z≈17 is correct, it is a very dramatic advance. On the other hand, CEERS-1749 has three apparent neighbors with z≈5 (12.5 billion years). It is plausible that it is actually part of a cluster with this group, and the apparent more than three times higher redshift is an illusion. It is this uncertainty that has led Naidu and his co-authors to label CERES-1749 “the Shrödinger candidate galaxy,” currently the oldest known galaxy and billions of years younger.
Even if CEERS-1749 is part of the z=5 cluster, it may still set a different record. To see what it looks like at az=5 distance, it must be a galaxy where star formation began and then largely ceased, or a smaller one unusually thick with dust (a preprint from another team also proposes the small and dusty stage). In these cases; “It will be the highest redshift quiescent galaxy, or one of the lowest-mass dusty galaxies of the early Universe detected so far,” write Naidu and his co-authors. Both would also challenge existing models of galactic evolution, if not as profoundly.
It is probably the second possibility that led Naidu to cryptically tweet:
Nine days later he shared the preprint. As a field, astronomy has probably never moved as fast as it has in recent weeks.
If galaxies at redshifts of 5 are supplanting something much older, it would present a major challenge to cosmologists. However, the authors conclude: “Such a perfectly disguised contaminant is only possible in a narrow redshift window (∆z < 0.1)." A co-author he commented it also requires specific combinations of telescope filters, so it’s unlikely to be a factor we need to worry about often.
“Spectroscopic monitoring of this remarkable galaxy is of critical urgency to JWST’s mission to expand the cosmic frontier … if this source is found at az ≈ 17, we can embark on the grand enterprise of revising the phys. of the evolution of galaxies at the earliest times,” the authors write. Unfortunately, the world’s most valuable telescope time is not easy to come by.
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