I The impact of early galaxy formation on the CMBR

[pinball1970]

TL;DR Summary

Massive early-type galaxies contribute a non-negligible source of CMB foreground contamination. Even in our most conservative estimates, massive ETGs account for 1.4% up to the full present-day CMB energy density.

The impact of early massive galaxy formation on the cosmic microwave background​

The paper here.

https://www.sciencedirect.com/science/article/pii/S0550321325001403?via=ihub

From the conclusions

"What results from these estimates, naturally but unexpectedly, is as follows. Under the most conservative assumptions – i.e., assuming that the average ETG separation {D0 (nought)} in local volumes applies to the whole Universe – the formation of massive ETGs may account for 1.4% of the observed (present-day) CMB photon energy density. If, instead, (D0) corresponds to that inferred around Z~2 [32], then the cumulative energy density of massive ETGs would be of the same order as that of the observed CMB (Fig. 5). Assuming that dust produced by massive ETGs reaches thermal equilibrium with the ETG radiation field, the resulting emission would form a background near Z~15 that, when redshifted, appears to observers at Z=0 as a microwave photon field (Sec. 3.2). The independent data now coming from the observations with the JWST of the formation of massive galaxies at Z>9 and the ALMA observations of high-redshift, dust-rich, star-forming galaxies support this conclusion, as do the recent observationally obtained mass-growth times and rates of individual elliptical galaxies (Fig. 3)."

 

[Cerenkov]

Hello.

Could someone with an expert eye please help me understand more about this paper, what the authors are saying and what it could mean regarding our understanding of the CMB?

To my untrained eye it appears to be saying that some or much of what has been taken as the presence of the CMB could in fact be the presence of dust generated by early galaxies.

Which, according to my naïve and inexpert understanding of cosmology, appears to cast some doubt on the role of the CMB as evidence for the Big Bang, which preceded it.

Any help given to at a Basic level would be very much appreciated.

Thank you,


Cerenkov.

 

[pinball1970]

Hello.

Could someone with an expert eye please help me understand more about this paper, what the authors are saying and what it could mean regarding our understanding of the CMB?

To my untrained eye it appears to be saying that some or much of what has been taken as the presence of the CMB could in fact be the presence of dust generated by early galaxies.

Which, according to my naïve and inexpert understanding of cosmology, appears to cast some doubt on the role of the CMB as evidence for the Big Bang, which preceded it.

Any help given to at a Basic level would be very much appreciated.

Thank you,


Cerenkov.

Yes I should have said that also!

The paper was discussed elsewhere by non technical people like myself and would like to know the pf community think.

How significant is this reported 1.4%?

Will this result affect anything else? Like the Hubble calculation?

The earliest galaxies are now around Z=14 plus, this is still a long long way from Z=1110 are they not able to factor our this contribution via time emitted?

How close is the ETG to CMBR in terms of signal? SPD?

 

[Cerenkov]

Indeed, pinball1970! Would like to know and understand more.


But, using the following logic, I don't see how the early galaxy dust can be masquerading AS the CMBR.

Baryon Acoustic Oscillations have been detected spread across the sky.
According to my naïve and inexpert understanding these are evidence that the very early universe was filled with a superhot plasma. The very thing you would expect after the Big Bang. So, unless this early galaxy dust can somehow also cause galaxies to group in the ways that BAO's do, then the existence of the CMBR cannot be challenged by this dust.

But hey! What do I, as a rank amateur, know about how these things work?

It would be great if some of the big guns here could unpick this in a way that we can follow.


Cerenkov.

 

[PeterDonis]

CMB photon energy density

I see this term used throughout the paper, but what I don't see is any discussion of the frequency spectrum of the CMB vs. the predicted radiation from "early-type galaxies". But the frequency spectrum of the CMB--a black body spectrum with a current observed temperature of 2.7K--is a crucial factor in our interpretation of this radiation. I don't see anything in this paper that explains why we should expect radiation from ETGs to exactly mimic this single black body spectrum; the paper only talks about total energy density of radiation. The paper's authors appear to believe that total energy density is sufficient to derive a temperature--but it's not, and we don't derive the temperature of the CMB just from looking at total energy density, we derive it from the frequency spectrum. So it seems to me that there is a huge missing piece in this paper that's not addressed.

 

[Ibix]

but what I don't see is any discussion of the frequency spectrum of the CMB vs. the predicted radiation from "early-type galaxies".

I think that's what section 2.3.3 purports to do - show that the radiation is thermalised by its interactions with dust, which is much higher density in the early universe in this model compared to $\Lambda$CDM due to the rapid formation of galaxies. It does note that it's a fairly simple model and needs further study.

I'd add that they do seem to be explicitly using FLRW cosmology, so I don't think they're proposing an alternative cosmology. I think they are saying they think there's a large noise source in the data that we need to correct for. Obviously that would affect our estimates of cosmological parameters, and that might alter the playing field for detailed models, but I don't think they're saying the Big Bang CMB isn't there.

 

[PeterDonis]

the radiation is thermalised by its interactions with dust

Yes, I see that, but to get the radiation to be thermalized to the same temperature as the CMB at the same epoch seems to require a very precise fit of parameters--the thermalization has to happen entirely over a very short time period at just the right redshift (which looks to be about z = 17). That seems highly implausible to me, and what's more, it seems inconsistent with the data, which seem to show these ETGs over a fairly significant range of redshifts. That would seem to predict an observed spectrum now that would be a mixture of thermalized black body radiation at a range of different temperatures now, which won't look like a black body at a single temperature.

I don't think they're saying the Big Bang CMB isn't there.

I'm not sure the paper is making a single consistent claim. Sometimes it appears to just be saying there's this noise source in the data that needs to be taken into account, yes. But other times it appears to be saying that this source could account for all of the observed radiation that we currently attribute to the CMB.

 

[Ibix]

But other times it appears to be saying that this source could account for all of the observed radiation that we currently attribute to the CMB.

Well, I think they say that they say their dust signature could "approach" the power of the CMB.

But, at the same time, they explicitly say at the beginning of section 2 that they're using a $\Lambda$CDM framework unless otherwise noted and they seem to be using the concept of expanding space, so I don't see how they can not have an early hot dense phase and hence an EM background.

I think maybe they're trying to cast as wide a net as they can in terms of implications, so if anything comes of it they can claim priority. I don't really have a sense of how likely it is anyone else will take this seriously, but I note it's in Nuclear Physics B, which seems like an odd title to publish cosmology.

 

[Ibix]

the thermalization has to happen entirely over a very short time period at just the right redshift (which looks to be about z = 17).

Does it? Or does it just have to stop happening abruptly at z=17? Isn't their model essentially analogous to the pre-recombination universe, but with partial opacity from dust instead of primordial plasma, and heat from the galactic formation instead of inflaton field phase change or whatever? So what we'd be looking for in the paper is an analogue of the last scattering surface - i.e. some sort of claim that the dust abruptly vanishes (or stops being opaque anyway) at z=17. The thermalisation would stop then, leaving a second CMB.

 

[PeterDonis]

Does it?

Yes, because the temperature at the time of thermalization shouldn't depend on when (at what redshift relative to us here and now) the process happens; it depends on factors that are independent of that. So unless the thermalization happens at just the right redshift, the thermalization temperature won't match the CMB temperature.

To put it another way: say the temperature at the time of thermalization is 50 K, based on the factors involved. Then thermalization at redshift z = 18 (about--the paper says z = 17 for this temperature, but I can't make that match) will match the CMB temperature at that redshift. But thermalization at, say, z = 19 won't. Or, looking at it from our standpoint here and now, we wouldn't just see one black body in our data: we'd see two, one with a temperature of 50 K divided by 18 (i.e., the CMB temperature we actually observe), and one with a temperature of 50 K divided by 19 (i.e., lower than the CMB temperature we actually observe). So unless the thermalization happens only at z = 18, it won't match what we actually observe.

 

[Cerenkov]

Ummm... my thanks go out to Peter Donis and Ibix for their comments.


Buuut... would it be possible for your conversation to be translated into terms that pinball1970 and I are more likely to understand?

We are keen to comprehend more.


Thank you,


Cerenkov.

 

[Ibix]

would it be possible for your conversation to be translated into terms that pinball1970 and I are more likely to understand?

They propose that early galaxy formation produced a lot of EM radiation and heavy dust. The radiation bounces around in the dust and the radiation and dust reach an equilibrium temperature (and hence a blackbody spectrum) before the dust thins (or something) enough to become transparent. Then the radiation escapes and we (a long time later) see a blackbody source on the sky. The paper contends that this will be more or less a uniform glow and (more or less by coincidence, I think) have the same temperature as the CMB. So if we believe their model at all we need to work out how bright that is and subtract it from the CMB when we're studying that, just as we do with other foreground sources. It's only tricky because it's a noise source that the authors say would closely mimic the CMB signal.

Peter is very sceptical because he thinks all the different sources will have the same emission temperature but at different times and hence different redshifts, so the total glow would have many different apparent temperatures and wouldn't be a unique blackbody. I want to look at the paper again - I understand his point, but it's such an obvious problem I can't see how the authors would miss it. On the other hand, I wonder how much cosmology gets published in a Nuclear Physics journal, so perhaps that's a sign of something.

 

[Cerenkov]

Thank you very much Ibix.


That's very helpful.

Picking up your last sentence and wondering about the 'signs' associated with the paper, I see that Sabine Hossenfelder has something to say about it on her YouTube channel.



Do you have any thoughts or comments about what she says?


Cerenkov.

 

[ThickTarget]

I'm going to post something I wrote elsewhere. This addresses some of the discussion here, but I'm to lazy to completely rewrite it. Apologies for arriving late:

First thing to stress, the paper is not using standard cosmology. Secondly, if you open the paper you will see that it contains exactly zero JWST data. Some have got the impression that this paper implies JWST results are in conflict with standard cosmology, but it's not that at all.

So what is their calculation based on? The answer to that is many assumptions pulled out of thin air, with little regard for observations or physics. Their basic assumption is that the massive elliptical galaxies we see today in the local universe all formed immediately in the early universe, redshift 15 to 20. So even higher than any confirmed JWST galaxy. In their model, the take an simplistic model of galaxy formation (monolithic collapse), which is sometimes invoked by MOND people. Note that in standard cosmology you have hierarchical structure formation where small galaxies formed first, they are essentially assuming top down growth, it's not standard at all. They also assume that these galaxies are miraculously totally enshrouded by dust. The dust is then conveniently destroyed. They then get a "background" which is comparable to the CMB. The problem is it's all based on these untested assumptions.

The paper never asks if these assumptions actually correspond to reality. For that, we can turn to observations. Firstly, it violates JWST observations. The most distant confirmed galaxy has a mass of 10^8 solar masses in stars. These galaxies would be 10^11.5 and above. There are no high redshift candidates that are anywhere near this massive. In their model, these become passive (quenched) galaxies at lower redshift. The number density of such objects measured by JWST is at least a factor of 100 lower than they require, even ignoring the fact that there is this huge discrepancy in mass. They don't consult JWST luminosity functions, or number densities, they don't ask if what they assume is real. It would also require the number of massive galaxies to be constant at all redshift, whereas observations show a steep decrease. Based on JWST alone, it's ruled out.

The paper doesn't bother to calculate what spectrum these galaxies would emit. One heading within the paper says that dusty galaxy spectra resemble blackbody, which is true, but they're also clearly wrong. In real dusty galaxies you get absorption and re-emission by the dust (radiative transfer), giving rise to a modified blackbody (greybody). The authors have confused dust temperatures with real blackbodies. My image is the far infrared SED of a local ULIRG Arp220. The red line is an assumed blackbody, the black dotted line is a modified BB. If the CMB were significantly contaminated by dusty star forming galaxies, it would mess up the spectrum. There are extremely tight limits on the spectrum from COBE FIRAS.



The paper says observers should look for this contamination. But they already have. Something which is (incredibly) not even mentioned is the Cosmic Infrared Background. The CIB is the cumulative effect of dusty star forming galaxies over cosmic time. The CIB is not like the CMB in that with enough resolution it can be separated into individual galaxies, it's also not a blackbody. The CIB has about 3-4% the energy compared to the CMB. In a press release Kroupa makes the suggestion that maybe this light is the whole CMB. Which is just wrong. In the paper they calculate there are just 6 source galaxies per Planck resolution element. So higher resolution telescopes like SPT, ACT, LMT and ALMA would easily resolve this background into individual galaxies. Which doesn't happen. If it were true ALMA would not be able to use the CMB to measure clusters via the SZ effect, because it would resolve it into one or two bright galaxies.

The paper is just a simple calculation based on many assumptions that are never justified. None of it is motivated by observations. It can also be rejected just with the data that exists today. It's missing cosmological context. In galaxy formation simulations it takes a long time for fluctuations to grow until galaxies can collapse. They aren't using simulations to calculate the full physics.

 

[Cerenkov]

Thanks very much for your fascinating input, Thick Target.


If you don't mind, I'd like to ask some questions.
Please bear in mind that I understand these things at a Basic level and that I'm an untrained amateur who simply possesses a keen interest in cosmology and astrophysics. So, if I err or make a rookie-level mistake, please take that intoaccount.

You say that this paper contains exactly zero JWST data.

For the sake of clarification and to further my understanding, what do you mean by this?

Abstract
Keywords
1. Introduction
2. Method
3. Results
4. Discussion
5. Conclusions
Declaration of Competing Interest
Acknowledgements
Data availability
References

Above if the way that Gjergo and Kroupa break their paper down into sections. Do you mean to say that no JWST data has been included in the Method? Which, according to my naïve thinking, should be where such data is used. Am I understanding things correctly here?


A brief search of their References does reveal three citations relating to the JWST.

https://arxiv.org/abs/2504.05893
Pushing JWST to the extremes: search & scrutiny of bright galaxy candidates at z ~ 15-30

https://arxiv.org/abs/2210.14915
Has JWST already falsified dark-matter-driven galaxy formation? (Pavel Kroupa contributes)

https://arxiv.org/abs/2203.07733
Implications of the cosmological 21-cm absorption profile for high-redshift star formation and deep JWST surveys


Thank you for any help given.


Cerenkov.

 

[Fredbonyea]

Several decades ago, I decided to see what the background might look like if the universe is infinite. As light travels, there are a few obstacles: 1) Dust, thought to be minor, on the grand scale it will creating a peak in the infrared. 2) Lyman absorption lines due to neutral cold H2 and 3) Amplification in select bands because of the semi-stable states of Helium. I found that when I used Chandrasekar's radiation transfer equation to integrate light about these 'notch' filters over cosmic distances, an infrared and a microwave background emerges that was similar to what we observe today.

My point is, it is difficult to say with any certainty that the background we observe can be pinned down to a specific time or point of origin. These authors have reached a similar conclusion - early mature galaxies fog the issue. It is no longer kosher to argue the power structure of the background describes a specific origin: There is way too much tension in the extrapolations that the LCDM model was created to accommodate.

 

[renormalize]

I found that when I used Chandrasekar's radiation transfer equation to integrate light about these 'notch' filters over cosmic distances, an infrared and a microwave background emerges that was similar to what we observe today.

Is this just personal analysis (which is off-limits for discussion on Physics Forums)? If it's not, can you cite where this work is published? Thanks.

 

[ThickTarget]

Above if the way that Gjergo and Kroupa break their paper down into sections. Do you mean to say that no JWST data has been included in the Method? Which, according to my naïve thinking, should be where such data is used. Am I understanding things correctly here?


A brief search of their References does reveal three citations relating to the JWST.

When I said data, I mean something quantitative. This could be using JWST data directly, or other people's measurements. Citing papers is not the same thing as using data. They could have lifted measurements from these papers, and test how their model corresponds to observations. Like comparing how many galaxies their model predicts compared to the observed luminosity functions. Or how the properties of their modeled galaxies compare to real ones. Or use real data as the input for their model. But they didn't do any of this. They also don't calculate observable (e.g. magnitudes, luminosity functions, number densities) which could be tested against JWST data in the future. Again, they did not. So they said this was inspired by JWST, but it is really only at the qualitative level.

My point is, it is difficult to say with any certainty that the background we observe can be pinned down to a specific time or point of origin.

The CMB fluctuations are pretty damning evidence that the CMB is the relic of a hot big bang. Before anyone could measure it theorists had calculated the detailed statistics of the fluctuations on different scales, and the polarisation. The CMB was confirmed to exist, then it was confirmed to have a precise blackbody spectrum. Then experiments like Planck have measured the fluctuations in detail revealing the imprints of acoustic sound waves in the primordial plasma, just as had been predicted by theory.



Today there are exactly zero alternative models which can explain any of this without a big bang and recombination. This new paper has not changed that. Standard cosmology may be ruled out, but that doesn't mean the CMB is necessarily produced by some other mechanism.

 

[Cerenkov]

While waiting for Thick Target to reply, I was wondering if any other members would like check the logic of this following argument?


1. Baryon Acoustic Oscillations have been detected spread across the sky.

2. According to Wikipedia... In cosmology, baryon acoustic oscillations (BAO) are fluctuations in the density of the visible baryonic matter (normal matter) of the universe, caused by acoustic density waves in the primordial plasma of the early universe.

3. Therefore, unless BAO's can be attributed to something else, the fact that we observe them should be a valid line of evidence for the existence of the primordial plasma.

4. This plasma created the surface of last scattering, which we now observe as the CMBR.


Have I overlooked something or misunderstood something or is the logic of my argument sound?


Thank you,


Cerenkov.

(Cross posted. Thank you Thick Target!)

 

[pinball1970]

3. Therefore, unless BAO's can be attributed to something else, the fact that we observe them should be a valid line of evidence for the existence of the primordial plasma.

From what I have read, surveys look how galaxies cluster in 3D

https://sci.esa.int/web/euclid/-/what-are-baryonic-acoustic-oscillations-

 

[Cerenkov]

Thanks for this pinball1970!


Yes, that link is very helpful and, as far as I can tell, agrees with the logic I've employed in the argument I posted on Thursday.

The BAO's we observe today require the existence of the primordial plasma in the very early universe.

And the CMBR was emitted from the last scattering surface of this plasma.

That all seems to hang together logically from my naïve p.o.v.

But, this being science, all things must be tested, so it would be nice if my argument could be looked at by those who know much more about these matters than I do.

Anyway, thanks again pinball1970.



Cerenkov.