Early large galaxy studies

[pinball1970]

TL;DR Summary

The standard model for how galaxies formed in the early universe predicted that the James Webb Space Telescope would see dim signals from small, primitive galaxies. But data are not confirming the popular hypothesis that invisible dark matter helped the earliest stars and galaxies clump together.

"What the theory of dark matter predicted is not what we see," said Case Western Reserve astrophysicist Stacy McGaugh, whose paper (12.11.24) describes structure formation in the early universe.

McGaugh, professor and director of astronomy at Case Western Reserve, said instead of dark matter, modified gravity might have played a role. He says a theory known as MOND, for Modified Newtonian Dynamics, predicted in 1998 that structure formation in the early universe would have happened very quickly—much faster than the theory of Cold Dark Matter, known as lambda-CDM, predicted.

https://iopscience.iop.org/article/10.3847/1538-4357/ad834d (open access)

There was also this in Nature (abstract only)

https://www.nature.com/articles/s41586-024-08094-5 (13.11.24)

A survey of 36 galaxies that yielded "three ultra-massive galaxies (logM★/M⊙ ≳ 11.0, where M★ is the stellar mass and M⊙ is the mass of the Sun) require an exceptional fraction of 50 per cent of baryons converted into stars—two to three times higher than the most efficient galaxies at later epochs."

and "The contribution from an active galactic nucleus is unlikely because of their extended emission."

Possibly a reference a couple of studies like the below in the last few months,

https://iopscience.iop.org/article/10.3847/1538-3881/ad57c1

 

[ohwilleke]

FWIW, the prediction of early structure formation with MOND is pretty generic to all gravity based explanations of dark matter phenomena.

Do Early Galaxies And The Hubble Tension Have A Common Source?

Early structure formation could also be related to the Hubble tension which is equally glaring. There are basically three ways to resolve the Hubble tension (and a solution could come, in part, from two or more of them and not just one):

1. Early CMB based calculations of the Hubble tension are off by about 9%.

McGaugh, for example, has suggested that this is a plausible full or partial explanation (although he hasn't explicitly made the connection between this possibility and early structure formation in anything that I've seen him write, as I spell out in the paragraphs in bold below).

For example, maybe the Planck collaboration omitted one or more theoretically relevant components of the formula for converting CMB observations to a Hubble constant value that were reasonably believed to be negligible (indeed, it almost certainly did so). But it could be that one or more of the components omitted from the Planck collaboration's calculated value of Hubble's constant from the CMB data actually increase the calculated value by something on the order of 9% because some little known factor makes the component(s) omitted have a value much higher than one would naively expect.

Also, since the indirect determination of the value of Hubble's constant from CMB measurements is model dependent, any flaw in the model used could cause its determination of Hubble's constant to be inaccurate.

An indirect CMB based determination of Hubble's constant is implicitly making a LamdaCDM model dependent determination of how much the universe had expanded since the Big Bang at the time that the CMB arose. If the LambdaCDM model's indirect calculation of Hubble's constant predicts that the CMB arose later than it actually did, then its indirect determination of the value of Hubble's constant would also be too low, and a high early time value of Hubble's constant would resolve the problem.

This is a plausible possibility because the James Webb Space Telescope has confirmed that the "impossible early galaxies problem" is real, implying that there is definitely some significant flaw (of not too far from the right magnitude and in the right direction) in the LambdaCDM models description of the early universe, although the exactly how much earlier than expected galaxies arose in the early universe (which is a mix of cutting edge astronomy, statistical analysis, and LambdaCDM modeling) hasn't been pinned down with all that much precision yet.

The impossible early galaxy problem is that galaxies form significantly earlier after Big Bang than the LambdaCDM model predicts that they should. The galaxies seen by the JWST at about redshift z=6 (about 1.1 billion years after the Big Bang) are predicted in the LambdaCDM model to apear at about redshift z=4 (about 1.7 billion years after the Big Bang).

If the CMB arose more swiftly after the Big Bang than the LambdaCDM model predicts it did but the amount by which the universe had expanded at that point was about the same, in much the same way that galaxy formation actually occurred earlier than the LambdaCDM model predicted that it would, then that could fully or partially resolve the Hubble tension.

The relationship between Hubble's constant and the amount of expansion in the universe at any given point in time is non-linear (it's basically exponential). So, figuring out how much of a roughly 55% discrepancy at 1.1 billion years after the Big Bang in galaxy formation time translates into in Hubble constant terms, at about 380 million years after the Big Bang, is more involved than I have time to work out today, even though it is really only an advanced pre-calculus problem once you have the equations set up correctly. But my mathematical intuition is solid enough to suspect that the effect isn't too far from the 9% target to within the uncertainties in the relevant measurements.

2. Late time measurements of the Hubble tension are off by about 9%. But this is complicated by the fact that the late time measurements are confirmed by independent methods, so the source of the inaccuracy in the late time measurement would have to be due to a systemic error source common to all of them.

For example, one explanation that has been explored is that the little corner of the universe around the Milky Way from the perspective of solar system observers has some local dynamics, or has local distortions that impact light at the relevant wavelengths reaching us in the solar system (e.g. due to localized gravitational lensing or local distributions of interstellar gas and dust) that has nothing to do with the expansion of the universe, but is indistinguishable, by the most precise existing methods used to measure Hubble's constant in the late time universe, from an increase in Hubble's constant of about 6.4 (km/s)/Mpc.

3. There are new physics that explain it.

Another Possible Cause Of The Impossible Early Galaxies Problem

Another point related to the impossible early galaxies problem which hasn't, IMHO, received enough attention, is that star formation within galaxies appears to happen about ten times faster than expected, probably as a result of the influence of weak magnetic fields in star forming galaxies. See T.-C. Ching, et al., "An early transition to magnetic supercriticality in star formation" Nature (January 5, 2022) (open access) https://doi.org/10.1038/s41586-021-04159-x

It takes much longer for galaxies to coalesce from individual stars (on the order of hundreds of millions or billions of years) than it does for stars to form from hydrogen gas. The "classical view" is that it takes about ten million years for a typical star to form, while the observations in the article cited above, suggests that one million years is closer to the mark.

I have blogged this article and quoted secondary materials discussing it that post.

Given that we're only looking for a tweak of 9% or less to the current inference of the early time Hubble constant value from the CMB observations (about 0.1 dex in the terms astronomers like to use for uncertainties), it doesn't have to be a huge effect.

This star formation timing issue may very well be completely independent of the impact of dark matter and/or gravity based explanations for phenomena attributable to dark matter on how long it takes galaxies to form. And, while a star formation issue would still be a problem with the LambdaCDM based model of how galaxies form, it isn't a core assumption of the LambdaCDM model and could be incorporated into predictions of how long it takes galaxies take to form in the LambdaCDM with this one modification without greatly disturbing the other cosmological predictions of LambdaCDM.

On the other hand, it could be that some of the discrepancy between theory and observation in star formation rates could have a full or partial cause related to gravitational effects that explain dark matter phenomena that Ching (2022) does not consider as a possible explanation.