astroH

a lot better...we can excite these atoms in a lab and simply measure what comes out. often times don't even need a model because spectroscopy can be fully empirical for many transitions

And so you have proved my point. The observations presented in this article can be made consistent with both...as such one should think about stronger tests of both LCDM and MOND.

This is a misrepresentation of what I am saying. By no means am I casting an aspersion on JWST. I am casting an aspersion on this particular observation as a test of MOND and LCDM. Also I highly disagree about your comments on my line of reasoning. The fact that you can obtain a huge range of possible galaxy properties in the context of LCDM indicates that in general, tests of LCDM and MOND that rely on galaxy formation model are in usually not strong tests. This is the key issue with using the abundance of high-z galaxies (or even their masses -- despite the fact that these aren't measured) as a test. In the context of LCDM, you need haloes to form galaxies but it has been shown many times that there are enough haloes to solve the problem (see the paper linked) by a huge amount.

So I think it is fair to say they did exist. If we believe in Big Bang Nucleosynthesis then heavy elements had to come from somewhere making the first generation of stars (whatever their properties may be) be Population III. I agree that without a catalyst it's hard to initiate the CNO cycle but indeed models predict that it is possible even under these circumstances.

Multiple generations is perhaps an overstatement. The first oxygen in the Universe came from what we call Population III stars which is the first generation of stars to form after the Big Bang and what separates these from other stellar populations is that they do not have elements heavier than hydrogen or helium (except for minuscule traces left over from the Big Bang but these are insignificant). Now we don't know much about Population III stars but many models predict they are massive and when they die, can release 60 times the mass of our sun in the form of oxygen. That's really a lot of oxygen so you don't need too many of these to go off to pollute the early Universe and probably one of the reasons why we haven't yet found Population III stars.

I wouldn't say it's too damaging yet. There is a general trend where these early galaxies are brighter than we had thought by simply extrapolating models that were built prior to JWST, but these make numerous assumptions on how efficiently stars can form and the properties of these stars. Mildly relaxing any of these assumptions can easily solve the problem within our current framework and not significantly change what happens later in the evolution of the Universe.

It's a lot less sophisticated than that. They take images in multiple filters. In the context of JWST of order 10 filters (sometimes more sometimes less). Source extraction is then performed on the images by essentially identifying bright spots and dropping an aperture (separating ones that are nearby and blended if possible). The standard tool for this is called source extractor. They then have catalogs of tens of thousands of sources per image and the next step is to figure out redshift. There is a lot of code to do this but the simplest methods require fitting templates of what we think galaxies look like to these catalogs. High redshift sources tend to "drop" out of filters at shorter wavelengths. This is because neutral hydrogen in the early universe essentially absorbs almost all of the light at shorter wavelengths than 1216 angstroms. So if a galaxy is at redshift 10, the flux should essentially be zero at all filters that cover wavelengths shorter than 1.33 microns. JWST has filters both bluer and redder than this wavelength so we see the source appear in the redder filters and not the bluer ones. This technique was pioneered in the mid 1990s. This gives an approximate redshift called a "photometric redshift". There are other features in a galaxy spectrum that can mimic this "dropout" so not all photometric redshifts are robust. Therefore one has to take a spectrum of the galaxy which was what was done in this paper to confirm that the dropout is in fact the absorption feature we think it is. In this particular case, the authors were skeptical early on because there is a source right next to the object that is at a redshift where one of these other spectral features can mimic absorption by neutral hydrogen (this feature is the Balmer break). In any case, it's really an impressive demonstration of the power of JWST.

While in general, 'metal' means all elements except for hydrogen and helium, in this specific case, 'metal' really means oxygen. They are using the measurement of the [O III] 4363 line to estimate a gas temperature which allows for a determination of oxygen abundance but this gives no information on the other elements. One thing to keep in mind is that the method they use, while considered the gold-standard, is known to be biased such that metallicity is guaranteed to always be underestimated. Regardless, these galaxies are still metal-poor but it's not clear how well they mimic those in the early Universe which is one of the primary motivations for studying such objects.

Indeed, but we define their "metallicity" (mass fraction of elements heaver than helium) typically by the gas that they formed from. And the key point is that since they form from metal-free gas, you don't expect to see emission lines from metals which come from the star illuminating the surrounding gas with radiation.

These systems are very far away because you are looking more than 13 billion years back in time. The argument is JWST has a small field of view and these Pop III stars are like flashes in comparison to the age of the galaxy. So the probability of catching one that is bright enough to be detected is just super low. Which is why there is a strong prior that the HeII could be from other physics that is relatively well understood. But really the OIII emission is the biggest sign that this isn't a "primordial galaxy"

I think this is perfect! If only we can convince the author of the article...

Unfortunately not. These stars have no elements heavier than hydrogen and helium so you wouldn't be able to create a rocky planet that's habitable. Furthermore their lifetimes are only 3 Myr which is much to short to form a rocky planet and also the explosion from SN if it happens or direct collapse of the star to a black hole would immediately destroy any life.

As an expert in this space, I can confidently tell you that nothing about this observation is conclusive about the presence of the "First Stars" or what we call "Pop. III" Stars. By definition, the first stars are nearly completely devoid of elements heavier than hydrogen and helium. The spectra shows absolutely booming emission from Oxygen III ions at 5007A so there are heavy elements in the system and at best there is a mix of Pop III stars and more normal stars. The lifetimes of the stars are very short, ~3 Myr, so the chances of seeing them are very low which is likely the limiting factor (along with their brightness) and thus there is a strong Bayesian prior against seeing them with a narrow field of view. The mass of the system at 10^7.35 solar masses is much greater than what we expect from theoretical models that form Pop. III stars and you must ask how it's possible to not have any metals pollute the gas. The main piece of evidence for Pop III stars is HeII emission at 1640A which is a prediction of Pop. III stars, but you can also get this in many other ways, for example X-ray binaries. We see this plenty in the local Universe and we fully expect this to happen elsewhere. So to me this is headline chasing with little conclusive evidence.