This is an artist’s impression of JADES-GS-z14-0, which as of today is the most distant confirmed galaxy. Galaxies in the early Universe tend to be clumpy and irregular. Supernova explosions in this galaxy would have spread heavy elements forged inside stars, like oxygen, which has been now detected with the Atacama Large Millimeter/submillimeter Array (ALMA). Credit: ESO/ M Kornmesser.
Since its discovery last year, JADES-GS-z14-0 has been exciting astronomers the world over as it is the most distant confirmed galaxy ever found. Because it’s light has taken 13.4 billion years to reach Earth, it means we are looking at it in its infancy, when the Universe was less than 300 years old.
If that wasn’t enough, two near simultaneous studies came up with another astounding fact this year: there was an abundance of oxygen and other heavy elements which is unexpected in such a young galaxy. The discovery is making astronomers rethink how quickly galaxies formed in the early Universe. ScienceVega spoke to Leiden Observatory’s Sander Schouws to find out more…
ScienceVega: Can you give a little background to the story of JADES-GS-z14-0?
SS: Sure! To study galaxies astronomers have been using deep fields for quite a long time now. These are (small) parts of the sky which we have observed for a long time to get very deep data to find faint far-away sources. One of the famous ones is the Hubble Ultra Deep Field South (HUDFS) and this is part of a larger field called GOODS-South. They’re in the southern hemisphere of the sky, hence the emphasis on ‘south’ in both names.
Since this field has a lot of deep data from the Hubble space telescope (and also a lot of other observations from the ground and space, from X-rays to radio), when the James Webb Space Telescope was launched, it was a good target for more observations. One of these surveys of that field is called JADES.
The unique thing about JWST is that it observes at longer wavelengths than was possible with Hubble or with ground-based telescopes. This is important because for far-away galaxies their spectrum gets redshifted to longer wavelengths. Therefore, to be able to find these galaxies, you need to detect their light at these longer wavelengths.
JADES-GS-z14 was found in this new survey with JWST (the GS in the name actually refers to GOODS-South). It was found using the Lyman break technique, which is a point in the spectrum where suddenly a lot of light is absorbed by gas, resulting in a strong break in the spectrum. We know the wavelength of this break, so if we can measure in which filter the light of a galaxy suddenly disappears, we can estimate its redshift (and hence distance). Such an estimate is called a ‘photometric redshift’, because it relies on photometry – a fancy name for measuring the amount of light we measure from a source in a particular filter.
The photometric redshift is quite uncertain, that is why the source was observed again with JWST, this time with a spectrograph, to get a detailed measurement of its spectrum. That revealed the Lyman break of the source seen in this image. (Credit: S Carniani et al. https://creativecommons.org/licenses/by/4.0/.)
The spectrum of the galaxy is the black line and the strong jump in flux is the Lyman break. The yellow-green below is a 2d image of what the spectrum looks like on the detector (after calibration). The red squares in the inset image show the aperture through which the spectrum was observed.
Now, from this spectrum of the Lyman break we could approximately measure the distance, sufficiently good to use another telescope – ALMA – to confirm the distance very precisely. ALMA operates in a completely different part of the spectrum with light waves that have wavelengths with sizes around a millimetre. That kind of light can actually be observed from the surface of the Earth from special places, in this case the Atacama Desert in Chile. It’s also technically not a single telescope, but a large network of 45 telescopes that work together to form a very sensitive image.
With ALMA we detected the oxygen line (see image below) confirming the precise distance to the source with ~100x better accuracy, as well as learning a lot about the properties of this galaxy.
The inset in this image shows JADES-GS-z14-0 – the most distant known galaxy as of today – as seen with the Atacama Large Millimeter/ submillimeter Array (ALMA). The two spectra shown here result from independent analysis of ALMA data by two teams of astronomers. Both found an emission line of oxygen, making this the most distant detection of oxygen, when the Universe was only 300 million-years-old. Credit: ALMA (ESO/ NAOJ/ NRAO)/ S Carniani et al/ S Schouws et al/ JWST: NASA, ESA, CSA, STScI, Brant Robertson (UC Santa Cruz), Ben Johnson (CfA), Sandro Tacchella (Cambridge), Phill Cargile (CfA).
ScienceVega: How do we know this is the most distant confirmed galaxy?
SS: Galaxies that are this far away are very rare and also very difficult to find. Because they’re so far away they’re very faint and hard to detect. Also there are a lot of nearer galaxies that initially look similar to very far away galaxies. That means that you need to sort through a lot of candidates to actually find one of these unique galaxies.
Therefore, because it doesn’t happen often that the distance record is broken, all astronomers find out quite quickly when it happens. It actually happened again very recently, the new record is now slightly further at z=14.44. This new galaxy is a lot fainter than GS-z14 though, so it will be hard to detect with ALMA. I calculated it would probably take around 30 hours, while for GS-z14 we only needed around three hours.
In October 2023 and January 2024, an international team of astronomers used Webb to observe galaxies as part of the JWST Advanced Deep Extragalactic Survey (JADES) programme. Webb’s NIRSpec was used to obtain a spectrum of the distant galaxy JADES-GS-z14-0 in order to accurately measure its redshift and therefore determine its age. The redshift (14) can be determined from the location of a critical wavelength known as the Lyman break. This galaxy dates back to less than 300 million years after the big bang. Credit: NASA, ESA, CSA, J Olmsted (STScI), S Carniani (Scuola Normale Superiore), JADES Collaboration, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons.
ScienceVega: How can we detect oxygen in something so far away?
SS: Through emission lines. Every element has its own unique emission lines at particular frequencies. Some of these lines are faint and very hard to detect, others are stronger. These emission lines occur in all parts of the spectrum, from the X-ray to the radio and also in the sub-millimetre regime, which is where the oxygen line we looked at is located. From previous observations we have learned that it’s a strong line that has a lot of flux, so we expected there was a good chance we could detect it.
This infrared image from NASA’s James Webb Space Telescope’s NIRCam, part of the JADES program, highlights galaxy JADES-GS-z14-0. Credit: NASA, ESA, CSA, STScI, Brant Robertson (UC Santa Cruz), Ben Johnson (CfA), Sandro Tacchella (Cambridge), Phill Cargile (CfA), Public domain, via Wikimedia Commons.
ScienceVega: Is JADES-GS-z14-0 remarkable in other ways, or is there ongoing research that we need to wait for?
SS: The most remarkable thing about GS-z14 is that it’s very bright. That makes it a bit unexpected because to be so bright it must be forming a lot of stars at a very early age in the Universe.
Practically, the fact that it’s quite bright also helps a lot with doing observations, because the amount of time we need to detect something scales with the square of the luminosity of an object. So if something is half as luminous/ bright we need to observe it four times longer to detect it, and time on telescopes is limited.
So for both these reasons, it’s an ideal target to better understand the properties of some of the earliest galaxies in the Universe. In particular it will be observed again with JWST to look for emission lines in the optical part of the spectrum and for ALMA, we’ve proposed some exciting follow-up studies.
ScienceVega: In the field of astronomy, how does the sector respond when something like this is discovered?
SS: It’s always very exciting. JWST has really been a game-changer here, because for a long time the record was stuck at z~9-10. Within one year of JWST it was already pushed to z~13 and now z=14.44. Undoubtedly it’ll be broken again in the coming years.
ScienceVega: What research are you looking to do next?
SS: Regarding GS-z14, we have already done some follow-up observations looking for an emission line from carbon with ALMA. We did some quite deep observations and didn’t detect the line, which teaches us a lot about the extreme conditions in this source. I am also part of a proposal that’s asking to detect nitrogen in this galaxy and dust. Which is interesting because it would teach us more about how metals are formed from dying stars in very early galaxies.
Another thing that would be interesting to do, would be to observe the oxygen line in more galaxies that are similar to GS-z14. We have asked to do precisely this in a new proposal for the upcoming ALMA cycle and if we’re lucky the proposal will be accepted. We will find out in August.
Besides that I will be working on galaxies that are slightly less far away, but we suspect that they are the descendants of galaxies like GS-z14. By doing that we can learn more about their life cycle. In particular I’ll be looking at the neighbouring galaxies around our targets. Galaxies like to huddle together and by looking at how many neighbours a galaxy has, you can estimate how massive it is.
The link to the original paper can be found here.
