Metallicities over time/redshift - a community project?

[mikehelland]

Background: the standard model says that "early" galaxies should be metal-poor. Alternative models need to show metallicity isn't correlated to redshift.

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I made this page to show measurements of metallicity for local and "early" objects.

https://mikehelland.github.io/hubbles-law/other/metallicity.htm

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Update, May 10, 2024

I've been adding data and WOW, look at DESI in fuchsia!

I've also updated the tool to interactively turn on and off datasets.

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The measurements I've been collecting are $12 + log_{10}(O/H)$. I put them in a JSON file here, with their references, which is what builds the graph, table, and refs on the page:

https://github.com/mikehelland/hubbles-law/blob/master/data/metallicity.json

A community project?

If anyone has other measurements to add to this, I think you can just fork my project, make a change to metallicity, and do a pull request. Maybe we can make a compelling case against the metallicity-z relationship.

[Francois-Zinserling]

This is very interesting. I don't have much to add, but have some questions and maybe stimulate conversation?

• What I read is that distant (high redshift) galaxies, are presumed to be young stars/galaxies at time of emission, having low metallicity because metals take time to produce from Hydrogen. This is not observed, but results show that 'young' galaxies are more metallic that they should have been, and an almost absence of very low metallicity?
• 12+log(O/H) is a measure of the evolution of Oxygen into predominantly Hydrogen stars. Clearly log(O/H) is negative to get the results from your chart, and as one would expect because there is more hydrogen - almost always. The smaller O is, the bigger the subtraction. Then again from your chart it appears if there are a lot of low O stars/galaxies nearby, but erm ... almost none in the distance.

Am I at least understanding it right so far? Apologies - cosmology is not my strong field, despite my presence here in this group. :)

[mikehelland]

Sounds about right to me. I added another source that I found, it's the orange boxes:

So this does show more of what the mainstream predicts, as far as the earliest galaxies being lower in the metals. But, as you point out, the extremely metal poor galaxies are very near.

One thing to add is this:

The most reliable metallicity measurements are based on the flux ratio of the [O iii] λ4363 line against [O iii] λ5007. The technique is called the Te method, because it determines the electron temperature (Te) of the gas, and hence the gas-phase oxygen-to-hydrogen (O/H) abundance (Aller 1984; Izotov et al. 2006). However, detecting [O iii] λ4363 is difficult, because it is weak and almost undetectable in metal-rich galaxies.

https://iopscience.iop.org/article/10.3847/0004-637X/828/2/67

Measuring metallicity this way (O/H) seems to preclude metal rich galaxies. Apparently the line we use to detect O gets "washed" out if there is a lot of metal.

[RedshiftDrift]

Other ratios of spectroscopic lines are also related to metallicity, such as [Fe/H].

According to LCDM, young galaxies should mostly be found early (large z) in the universe, but galaxies are still being born today confirmed by low-metallicity galaxies at low redshift.

According to LCDM, old galaxies should mostly be found at low redshift. But since they have been finding old galaxies at high redshift, galaxy formation theoriest are struggling to find processes that could explain why mature-looking, high-metallicity galaxies. A large number of 'tweaks' are added to galaxy formation models. Some are:

1. an accretion rate larger than the "Chandrasekhar accretion rate", meaning that stars collect more gas than the quantity available to them,
2. a large population of black holes that improve the efficiency of star formation beyond what's normally possible,
3. other miracles of that type.

As usual, cosmologists don't see any problem with LCDM, they claim we need better 'galaxy formation' models.

[RedshiftDrift]

@mikehelland this is a nice graph showing no trend as a function of time. The hard part is to remove selection biases (e.g. high [O/H] galaxies might have an overall spectral colour that makes then harder to find at specific redshifts, with specific telescopes like Hubble...)

It is difficult for the non-expert to find data resources. You may write to the author of each paper and ask if they know about such a compilation, or if they know of a review paper that would list what is known so far.

[mikehelland]

Here's a video about metallicity that includes the graphs and data I found:

https://www.youtube.com/watch?v=RKso3RakFrU

Here's a "short" that basically does a montage kind of thing a measurements from 2004 to 2024:

https://www.youtube.com/shorts/6bIFuO13udY