Mature stars in ancient galaxies

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  • #1
turbo
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http://arxiv.org/PS_cache/astro-ph/pdf/0502/0502385.pdf [Broken]

Hence the galaxies SBM03#1 are already, to some ex-
tent, established systems. This is a significant finding since,
at z ≈ 6, the Universe is less than 1Gyr old.
No kidding. Would anybody here like to hazard a guess at where this "reddening dust" lies on the path between the z~6 galaxies and our vantage point? If the "reddening dust" is very ancient and distant, I would be interested in hearing how it could have been formed in the low-metallicity environment predicted by the BB theory. If it is more local, is there a model explaining the preferential reddening of distant galaxies?

Light should follow the same rules in distant environs as it does here. If not, the universe would look pretty strange. When we observe trends in the behavior of light, we should first explore the assumptions regarding the propagation of light in a "vacuum" before positing the existence of intervening materials, like "reddening dust", "iron fibers" (another weird but common one!) etc.

When light enters a denser propagating medium, it slows down, and when it encounters a less-dense medium, it speeds up. When it encounters a density transition that is not perpendicular to its direction of travel, it is bent. This is classical optics. Space is not empty, boys and girls. Space is a transmissive medium. That medium may not have boundaries as well-defined as those between the air/water surface of a swimming pool, but the properties of the transmissive media must be taken into account in any classical optical application, and we have not yet properly considered the role of the quantum vacuum as the transmissive medium (ether) through which EM propogates. If we are not willing to take this conceptual step, I believe that physics is going to be stalled for a very long time.

rant mode OFF
 
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  • #2
matt.o
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what are you on about? read section 3.5, they conclude that the models are best fit with no reddening due to dust.
 
  • #3
Chronos
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I vote with matt o. Dust models have long since been ruled out in the grand scheme of redshift corrections.
 
  • #4
turbo
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Chronos said:
I vote with matt o. Dust models have long since been ruled out in the grand scheme of redshift corrections.
Apparently not with these folks, since they made several critical comparisons with dust-reddening models in the course of their research. I'm happy that they managed to get good fits in their model without dust reddening, but am perplexed about how much significance they attached to it, if the idea is truly discredited.
 
  • #5
matt.o
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I'm sorry, but I think you really need to re-read the paper. The Calzetti reddening law is empirical and is proportional to the wavelenght of the light. They merely investigate the reddening to show the redness is caused by an older population of stars, not a dust reddened starburst. The reason they do this is because starbursts are known to be dusty, with intrinsic reddening increasing with star formation rate. They are trying to show that these galaxies had an older population of stars in place at this redshift, hence it is a relatively mature galaxy (for this epoch). They conclude that there must have been starbursts at an earlier epoch which may have helped reionise the early universe.
 
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  • #6
turbo
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I understand.

They also constrain the upper age of the mature star populations by saying that our theory says that the universe is 13.7GY in age and at z~6 the galaxies are less than a billion years old, thus the apparently mature stars must be under a billion years old. There are some models (Garth's included) in which the universe is considerably older than that, so it might be a good idea to constrain theory with observation, and not the other way around.
 
  • #7
SpaceTiger
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turbo-1 said:
I understand.

They also constrain the upper age of the mature star populations by saying that our theory says that the universe is 13.7GY in age and at z~6 the galaxies are less than a billion years old, thus the apparently mature stars must be under a billion years old.

No, that's incorrect as well. They determine a range of possible ages for the stellar population (250-650 Myr) by fitting stellar models to the spectrum. These are not dependent upon cosmology.

What is dependent upon cosmology is the formation redshift that these ages correspond to (z ~ 7.5 - 13.5). If early stars are responsible for reionization, then this is entirely consistent with the WMAP results, which imply that stars were forming as early as z ~ 17.
 
  • #8
matt.o
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turbo-1 said:
I understand.

They also constrain the upper age of the mature star populations by saying that our theory says that the universe is 13.7GY in age and at z~6 the galaxies are less than a billion years old, thus the apparently mature stars must be under a billion years old. There are some models (Garth's included) in which the universe is considerably older than that, so it might be a good idea to constrain theory with observation, and not the other way around.

Yes, they do. As Spacetiger has poined out, other observations point to a 13.7 Gyr old Universe. I don't see how a star-formation model could be used to accurately constrain the age of the Universe and overthrow the current models. As you can see from the paper, there are enough degeneracies in these models as it is. We don't actually know much about massive star formation, so using it to constrain cosmological parameters seems a bit far fetched!
 
  • #9
turbo
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OK, what does this mean?

paper said:
Figure 10. The allowed range of masses for several exponentially-
decaying SFR models for SBM03#1, with decay times ranging
from  = 10−1000Myr, as well as an instantaneous burst model
and a constant SFR model. Those with stellar ages > 1Gyr (right
shaded region) are ruled out (the Universe is younger than this at
z ≈ 6).
 
  • #10
matt.o
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What I am trying to say is that these models are ruled out based on other observational data. They are likely to be caused by some other degeneracy within the model, they should not be taken to mean the universe is older than 13.7Gyrs. You cannot make a SFR model with every parameter left to vary, there are too many degeneracies, hence you set the known parameters and constrain the unknown.
 
  • #11
SpaceTiger
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turbo-1 said:
OK, what does this mean?

Alright, you're correct, I overlooked that. What matt.o is saying is also correct, however. Fitting z = 6 spectra is extremely difficult without making some assumptions. :yuck:
 
  • #12
turbo
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SpaceTiger said:
Alright, you're correct, I overlooked that. What matt.o is saying is also correct, however. Fitting z = 6 spectra is extremely difficult without making some assumptions. :yuck:
Understood. If the LBT and the Webb allow observations of galaxies at z~8-10 and mature stellar populations are observed at those redshifts, what then? Do we simply ramp back the rapid star-formation epoch to z~22 and press on? That's the current trend, and it's disturbing.

We have already reached a point where observations should have made us reconsider our assumptions. We know that objects at z~6 exhibit solar and super-solar metallicities with no observed metallicity evolution with redshift. This makes perfect sense in a steady-state universe, but it is harder to reconcile with a Big Bang model in which metallicity must evolve - even in Garth's model, which is freely coasting and provides several billion more years of breathing room at the front end.

We do need to make assumptions, but I'm concerned that our assumptions are in need of some sober reconsideration.
 
  • #13
matt.o
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Your first paragraph is just irrelevant, as is the third. As for the middle paragraph, you seem to have failed to notice that the best fit models were the lower metallicity ones. Anyhow, I don't see the problem with high metallicities at z~6. We are obviously looking at objects undergoing extreme bursts of star formation and other activity. These bursts can last a few million years and heavily pollute a galaxy with metals very quickly. The extremely high star formation rates in these bursts could easily produce a population of older stars whilst the larger stars go supernova and pollute the ISM with metals.

Surveys out to z~6 are hardly complete and are extremely biased to the brightest of galaxies, so I don't see how you can make broad assumptions about metallicities and star formation of the universe at these redshifts. There is definitely not enough evidence to overthrow current cosmological models in favour of less likely ones.
 
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  • #14
Garth
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Yet matt.o and SpaceTiger, things are not that simple with the standard model; putting in some numbers:-

Using Ned Wrights calculator in the standard LCDM model, where tz=x to be the age of an object now observed at a red shift x, we have for time after BB:

For "re-combination" - the surface of last scattering of the CMB, z = 1089,
tz=1089 = 378,000 yrs.

for the onset of metallicity, i.e. Pop III stars, z = 20
tz=20 = 182 Myrs.
or SpaceTiger’s suggested figure of z = 17?
tz=17 = 229 Myrs.

for quasar 'ignition' z = 8 ??
tz=8 = 652 Myrs.

From that paper Spitzer Imaging of i'-drop Galaxies: Old Stars at z~6, for galaxy formation in the mass range 1.3-3.8x10^10Msolar z = 7.5 – 13.5
tz=13.5 = 318 Myrs. - tz=7.5 = 710 Myrs.

for 'modern' metallicity in Quasar SDSS J1030+0524 z = 6.28
tz=6.28 = 896 Myrs.

The real problem with star formation at high red shift is to explain how under gravitational collapse the
[tex]\frac{\delta\rho}{\rho} = 10^{-5}[/tex]
at last scattering became
[tex]\frac{\delta\rho}{\rho} = 10^{26}[/tex] or so,
in the early stars in only ~200 Myrs?

At z = 13.5 the average cosmological density is around 10-26 gm/cc and the mass of the observed galaxies ~ 1044 gms, so that mass would have had to be gravitationally scoured from a volume 1070 ccs, i.e. a radius ~ 135,000 lgt. yrs, in about 300 Myrs. i.e. at an average infall velocity of 0.05%c!

The earlier mature galaxies are discovered the more difficult it becomes to explain their formation in the time available.

Garth
 
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  • #15
Garth
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Garth said:
At z = 13.5 the average cosmological density is around 10-26 gm/cc and the mass of the observed galaxies ~ 1044 gms, so that mass would have had to be gravitationally scoured from a volume 1070 ccs, i.e. a radius ~ 135,000 lgt. yrs, in about 300 Myrs. i.e. at an average infall velocity of 0.05%c!
This may not be impossible, let us look further at the numbers. Without a detailed model of early galaxy formation we can only do an OOM calculation, but that itself may be illuminating.

First approximation: consider a steady in-fall acceleration. Note the real formation began at a very low acceleration and ended with a much higher one than in this approximation.

What constant acceleration would be required to form the observed galaxy in the mass range 1.3-3.8x1010Msolar in about 300 Myrs?

The infall distance was calculated to be 1.5x1023 cms and the time available is 3x108x3x107 secs i.e. ~ 1016 secs.

Now [tex]s=\frac12at^2[/tex], so [tex]a=\frac{2s}{t^2}[/tex], and putting in our numbers we get:
[tex]a=\frac{3.10^{23}}{10^{32}}=3.10^{-9} cm.sec^{-2}[/tex],

Reaching out to a range of 1.5x1023 cms this would require a dimensionless Newtonian potential of

[tex]\frac{GM}{rc^2}.\frac{c^2}{r}=\frac{GM}{r^2}=3.10^{-9}[/tex] so

[tex]\frac{GM}{rc^2}=3.10^{-9}.\frac{r}{c^2}=\frac{3.10^{-9}.1.5.10^{23}}{10^{21}}=5.10^{-7}[/tex]
This is actually equal to the dimensionless Newtonian gravitational potential of our own galaxy's field!

However the early galaxy is estimated to have a mass an order of magnitude smaller than our own, therefore a somewhat longer time than 300 Myrs. would appear to be required to allow it to form.

Just as a side note, and not wanting to bore anybody, the SCC/freely coasting time scales are about three times longer in this early epoch than the standard model.

Garth
 
  • #16
SpaceTiger
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To the best of my knowledge, the standard model has no trouble producing galaxies at z ~ 6. If you have a reference that suggests otherwise, please provide it.


However the early galaxy is estimated to have a mass an order of magnitude smaller than our own, therefore a somewhat longer time than 300 Myrs. would appear to be required to allow it to form.

Cold dark matter scenarios are "bottom-up", meaning that the small things form before the big ones. I suggest you read up on the Press-Schechter model of hierarchical growth. The original paper is here. Much has changed since then, but that paper outlines the basic approach. For updates, feel free to peruse the enormous list of citations.
 
  • #18
Chronos
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I'm guessing Garth is thinking about Jeans mass issues... an intersting topic. Any ideas about zero metallicity models? I am very interested in that subject. Dark matter adds to the fun. Curious, ST, I lean toward bottom up models, but I kind of like enormous black holes confusing the issue too. Is there a good way to constrain those models? Bear in mind I'm still a bit alarmed by 512 kev photons from the galactic core.
 
  • #19
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Chronos said:
Curious, ST, I lean toward bottom up models, but I kind of like enormous black holes confusing the issue too.

A good paper on early black hole growth can be found here. The high-redshift quasars are not inconsistent with current theory, but they are on the extreme end of it. As has been discussed previously, this could just be a selection bias.


Is there a good way to constrain those models? Bear in mind I'm still a bit alarmed by 512 kev photons from the galactic core.

I'm not quite sure what you mean. Are you referring to the radiation hypothesized to be due to dark matter annihilation?
 
  • #20
Garth
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SpaceTiger said:
To the best of my knowledge, the standard model has no trouble producing galaxies at z ~ 6. If you have a reference that suggests otherwise, please provide it.
Agreed for galaxies at z = 6, however I was simply supporting Turbo-1 and my comment that
The earlier mature galaxies are discovered the more difficult it becomes to explain their formation in the time available.
The reference is that referred to by Turbo-1 above: Spitzer Imaging of i'-drop Galaxies: Old Stars at z~6 which states
Exploring a range of population synthesis models indicates that the average stellar age is > 100Myr; our best-fit models suggest preferred ages of 250−650Myr for an exponentially-declining star formation rate (of decay time _ ≈ 70 − 500Myr) or a two-component model (with an ongoing starburst responsible for 0.5 − 5% of the total stellar mass). This implies formation epochs of zf ≈ 7.5 − 13.5 for the galaxies SBM03#1.
There is a problem in explaining the formation of 1010 Msolar galaxies at
z =13.5!

Chronos you are right in that I was thinking about the Jean’s mass, but primarily I was concerned about the time taken for such a mass to condense. Matt.o I think you must be mistaken, I only used a galactic mass 1010 Msolar in order to get a crude first approximation as to the lower limit of the time required. This can be illustrated more clearly using the free-fall time scale of a collapsing sphere that has satisfied the Jean’s criterion under homologous collapse.

[tex]t_{ff}=\sqrt{\frac{3\pi}{32G\rho}}[/tex]

for [tex]\rho=10^{-26}[/tex] (cgs units) we have tff = 0.67 Gyr.

So there is not enough time for such a body to form, even at their lower end of the z scale z=7.5 (0.71 Gyr)!

Garth
 
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  • #21
Garth
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We can be a little more accurate than that first approximation, although this is still a naive determination of a lower limit of the time for formation of objects in the early universe.

Using the standard model parameters the average cosmological density at z = 13.5 is

[tex]\rho=7.9.10^{-27} gm/cc[/tex] this gives a tff=0.75 Gyr..

At z = 7.5 the average cosmological density is [tex]\rho=1.6.10^{-27} gm/cc[/tex] this gives a tff=1.6 Gyr. making the situation worse!

Which shows the problem of forming anything, you have to start early.
Edit: These densities, of course are over-densities and in these naive calculations it is assumed that Jean's collapse is initiated when [tex]\frac{\delta\rho}{\rho} = 0.5[/tex].

Just for information in the SCC theory if you subsitute the density at z in tff and equate it with the universe's age at z you get a naive estimation of objects forming under Jean's mass homogolous collapse at z = 10.1. Edit: Furthermore, if we assume Jean’s collapse begins shortly after last scattering at z = 1000 when T = 3000K this model produces a Jeans Mass of 4 x 1010 MSolar that ends collapse at around z = 10 – exactly in the middle of that paper’s ball park!

Garth
 
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  • #22
SpaceTiger
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Garth said:
The reference is that referred to by Turbo-1 above:

No, the reference above is simply about observations. I'm asking for a reference suggesting that there's a problem with CDM predicting these galaxies. Your calculations are not sufficient, as they're completely incorrect.


There is a problem in explaining the formation of 1010 Msolar galaxies at
z =13.5!

The key thing to notice here is that they're suggesting the stars formed at that epoch, not necessarily the galaxy. Remember, in a bottom-up scenario, small things form first.


Chronos you are right in that I was thinking about the Jean’s mass,

The medium is not pressurized, so the Jeans mass is meaningless.


This can be illustrated more clearly using the free-fall time scale of a collapsing sphere that has satisfied the Jean’s criterion under homologous collapse.

[tex]t_{ff}=\sqrt{\frac{3\pi}{32G\rho}}[/tex]

for [tex]\rho=10^{-26}[/tex] (cgs units) we have tff = 0.67 Gyr.

This is incorrect as well because it ignores the accretion of matter onto the halo. This issue was directly addressed by Jim Gunn back in 1972. See here.


So there is not enough time for such a body to form, even at their lower end of the z scale z=7.5 (0.71 Gyr)!

I'm afraid the standard model has been saved yet again.
 
  • #23
hellfire
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SpaceTiger said:
This issue was directly addressed by Jim Gunn back in 1972. See here.
Hey, cool, this reference and the one of the original paper of Press and Schechter were very nice. May I suggest you to sum up some "historical" references about cosmology and astrophysics an post them in the "A&C Reference Library". I am sure every one of us would be grateful.
 
  • #24
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hellfire said:
May I suggest you to sum up some "historical" references about cosmology and astrophysics an post them in the "A&C Reference Library".

Sounds like a good idea. I'll see what I can do.
 
  • #25
Garth
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SpaceTiger said:
The key thing to notice here is that they're suggesting the stars formed at that epoch, not necessarily the galaxy. Remember, in a bottom-up scenario, small things form first.
Which part of
This implies formation epochs of zf ≈ 7.5 − 13.5 for the galaxies SBM03#1
do you not understand? (From that paper of observations of high z galaxies.) The stars were members of "a prominent older stellar population which probably dominates the stellar mass population" of these galaxies. (Italics my addition)
No, the reference above is simply about observations. I'm asking for a reference suggesting that there's a problem with CDM predicting these galaxies.
Yes, I was only referring to that paper, the model has to fit the observations, not the other way round. The baryonic gas in the early universe was pressurized, the pressure may have been low but so was the density, so the Jean's Mass and free fall time are relevant. Of course it is always possible to add in DM to make any model work, but until we know what that DM is the argument is hardly persuasive.

Garth
 
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  • #26
SpaceTiger
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Garth said:
Which part of do you not understand? (From that paper of observations of high z galaxies.) The stars were members of "a prominent older stellar population which probably dominates the stellar mass population" of these galaxies. (Italics my addition)

What they observed is an old stellar population in a ~1010 Msun galaxy at z ~ 6. However, this does not necessarily mean that the stars formed at the time that the 1010 Msun halo collapsed, since larger galaxies are theorized to accrete smaller ones, some of which can have pre-formed stars. The passage you quote does imply that the galaxies formed with the stars, but this is not necessarily correct in the context of current theories.

Nonetheless, even if the entire galaxy collapsed at z = 13.5, you still haven't shown that it's inconsistent with the standard model, nor have you cited any references that suggest a theoretical inconsistency.


Yes, I was only referring to that paper, the model has to fit the observations, not the other way round.

I think you know what I meant, but I'm going to repeat it just in case there's any doubt. Your calculations were wrong, so you haven't shown that the theory is inconsistent with the observations.
 
  • #27
Garth
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SpaceTiger said:
What they observed is an old stellar population in a ~1010 Msun galaxy at z ~ 6. However, this does not necessarily mean that the stars formed at the time that the 1010 Msun halo collapsed, since larger galaxies are theorized to accrete smaller ones, some of which can have pre-formed stars. The passage you quote does imply that the galaxies formed with the stars, but this is not necessarily correct in the context of current theories.
That paper does suggest that some observed galaxies at z = 6 are in some sense 'mature'. Again all I'm doing is to demonstrate, as I said above, that
Garth said:
The earlier mature galaxies are discovered the more difficult it becomes to explain their formation in the time available

SpaceTiger said:
Your calculations were wrong, so you haven't shown that the theory is inconsistent with the observations.
I have deliberately left out DM because we do not know what it is, my calculations were for baryonic matter, and if we leave out DE as well and reduce to a bare-bones Einstein-de Sitter model then the times available are much reduced also:

Using tz=x to be the age of an object now observed at a red shift x we have:

For "re-combination" - the surface of last scattering of the CMB, z = 1000,
tz=1000 = 300,000 yrs. in GR (Einstein-de Sitter)

for the onset of metallicity, i.e. Pop III stars, z = 20
tz=20 = 100 Myrs. in GR (Einstein-de Sitter)

for quasar 'ignition' z = 8
tz=8 = 350 Myrs. in GR (Einstein-de Sitter)

for 'modern' metallicity in Quasar SDSS J1030+0524 z = 6.28
tz=6.28 = 480 Myrs. in GR (Einstein-de Sitter).

Hence the standard model requires both DE to accelerate the universe and stretch out these times available for the formation of structure, early stars, quasars and galaxies, and also DM to accelerate the collapse of such structure and enhance the
[tex]\frac{\delta\rho}{\rho}[/tex] ratio, including, in particular, the time of last scattering and before.

But note we cannot have any DE around at the time of nucleosynthesis because that would stretch out that epoch as well and destroy the nice primordial abundances. So DE has to be switched off and on to fit.

I'm not disputing the model does then fit, my point here is only to point out that as earlier mature galaxies are discovered it becomes more difficult to 'tweak' the 'ad hoc' parameters of the amount and properties of the DE and DM required.

I'll grant you that when DE and DM are discovered in a laboratory, and their physical properties subsequently measured and found to be in agreement with what the cosmological model requires, then we have a theory. Until then it all smacks of being rather 'contrived'.

Garth
 
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  • #28
SpaceTiger
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That paper does suggest that some observed galaxies at z = 6 are in some sense 'mature'. Again all I'm doing is to demonstrate, as I said above, that

The earlier mature galaxies are discovered the more difficult it becomes to explain their formation in the time available

There is obviously a redshift at which the formation of galaxies would be hard to explain in lambda-CDM, just as there are a lot of hypothetical observations that would be hard to explain in any model. However, those observations have not happened (and probably never will), so why are you talking about this?


Hence the standard model requires both DE to accelerate the universe and stretch out these times available for the formation of structure, early stars, quasars and galaxies, and also DM to accelerate the collapse of such structure and enhance the
[tex]\frac{\delta\rho}{\rho}[/tex] ratio, including, in particular, the time of last scattering and before.

It seems that you've reworded what is actually a success for the standard model. Dark matter was hypothesized first as a solution to the problems regarding rotation curves and velocity dispersions, but as a bonus, it also turned out to resolve the problems with large scale structure. In more than just this respect, the growth of structure is among the more convincing evidence for dark matter (try comparing the CDM simulations with the SDSS LSS data when you get the chance, it's quite striking).

In short, the fact that you need DM for this to work is support for the model, not the other way around. I've not heard, however, that DE is required for consistency with LSS data. I would expect it to make little difference at such early times.


But note we cannot have any DE around at the time of nucleosynthesis because that would stretch out that epoch as well and destroy the nice primordial abundances. So DE has to be switched off and on to fit.

No! I'm actually surprised that you would get this wrong. [tex]\Omega_{\Lambda/DE}[/tex], the quantity of interest, is not a constant with time. In fact, you would need a very contrived dark energy model to make it significant at the epoch of nucleosynthesis.


I'll grant you that when DE and DM are discovered in a laboratory, and their physical properties subsequently measured and found to be in agreement with what the cosmological model requires, then we have a theory. Until then it all smacks of being rather 'contrived'.

I don't disagree that dark matter and dark energy are unsettling, but they fit the data and have even made successful predictions. There aren't yet any competing theories that can say the same.

Personally, I think the evidence is strong enough now that we should accept dark matter as the working model. In fact, only a very few astronomers really question it anymore. In retrospect, I think dark matter even satisfies the principle of mediocrity. After all, why should we assume that all matter in the universe would be visible to us? :wink:

As for dark energy, it's not even really a theory, it's just a parameterization for what we can't explain. I'm willing to entertain any guesses to what it might be at this point.
 
  • #29
Garth
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Thank you SpaceTiger for your comments, I will answer them carefully.
SpaceTiger said:
There is obviously a redshift at which the formation of galaxies would be hard to explain in lambda-CDM, just as there are a lot of hypothetical observations that would be hard to explain in any model. However, those observations have not happened (and probably never will), so why are you talking about this?
Because turbo-1 had a point, and galaxies with mature stars at z = 6, that could have formed at z = 13.5, may prove to be those "hard to explain in lambda-CDM".
It seems that you've reworded what is actually a success for the standard model. Dark matter was hypothesized first as a solution to the problems regarding rotation curves and velocity dispersions, but as a bonus, it also turned out to resolve the problems with large scale structure.
I do not dispute the existence of DM, only in its hypothetical more exotic non-baryonic form. Baryonic DM resolves the galactic rotation curves, binds galactic clusters and lenses distant quasars. In order to resolve the problems with large-scale structure you need "non-pressurized" non-baryonic DM with properties chosen heuristically to make it fit. It is this hypothesis that I will question until DM is discovered in a laboratory. That has not yet happened and not for want of trying!
In more than just this respect, the growth of structure is among the more convincing evidence for dark matter (try comparing the CDM simulations with the SDSS LSS data when you get the chance, it's quite striking).
I have, you will find a good resource of downloadable movies here. Notice that in the second and fifth movies that at z = 13.5 not much has happened. Most of the action takes place from z = 6 until the present epoch.
In short, the fact that you need DM for this to work is support for the model, not the other way around. I've not heard, however, that DE is required for consistency with LSS data. I would expect it to make little difference at such early times.
As you will have seen from my several posts on the subject the timescale in the standard Einstein-de Sitter model is too short for structure to form, even with non-baryonic DM. The hypothetical DE provides not only the acceleration necessary to fit the distant SN Ia data but also to stretch out these early time scales. My point all along is also to point out that, as it has been recognised by several researchers in the field, both are also fitted by a linear freely coasting expansion.
No! I'm actually surprised that you would get this wrong. [tex]\Omega_{\Lambda/DE}[/tex], the quantity of interest, is not a constant with time. In fact, you would need a very contrived dark energy model to make it significant at the epoch of nucleosynthesis.
That depends on the physical properties of DE: quintessence? leaky branes? cosmological constant? etc. etc.? These properties have been heuristically chosen to make the model fit.
I don't disagree that dark matter and dark energy are unsettling, but they fit the data and have even made successful predictions. There aren't yet any competing theories that can say the same.
There are, actually, such as the theory of Self Creation Cosmology published in the original paper here: On Two Self Creation Cosmologies, as the new theory here A New Self Creation Cosmology, and most recently here http://novapublishers.com/catalog/product_info.php?products_id=1869. The theory may be found for free on the physics ArXiv as well. It does fit cosmological constraints without invoking DE or exotic DM.
Personally, I think the evidence is strong enough now that we should accept dark matter as the working model. In fact, only a very few astronomers really question it anymore. In retrospect, I think dark matter even satisfies the principle of mediocrity. After all, why should we assume that all matter in the universe would be visible to us?
I agree, but why choose an unknown exotic form of DM when ordinary baryonic matter (now mainly in the form of IMBH's?) may do the job just as well?
As for dark energy, it's not even really a theory, it's just a parameterization for what we can't explain. I'm willing to entertain any guesses to what it might be at this point.
Likewise!

Garth
 
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  • #30
turbo
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SpaceTiger said:
As for dark energy, it's not even really a theory, it's just a parameterization for what we can't explain. I'm willing to entertain any guesses to what it might be at this point.
Obviously, not ANY guesses! :uhh: I've been down that road...

Right now, DE is simply a measure of how much BB theory needs to be "adjusted" in order to remain somewhat consistent with observation. Since this measurement has been given a cute name, some folks have been lulled into thinking that DE is a real entity just waiting to be discovered, and not simply a measurement of how far the BB theory falls short of agreeing with observations. I believe that this is a false hope, and that Dark Energy and non-baryonic DM will go away when the BB theory is supplanted with a theory that is reconcilable with quantum physics.

For a refreshing appraisal of this situation, download and view Rocky Kolb's SLAC lectures.

http://www.slac.stanford.edu/econf/C0307282/lecture_program.html
 
  • #31
SpaceTiger
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Garth said:
Thank you SpaceTiger for your comments, I will answer them carefully.Because turbo-1 had a point, and galaxies with mature stars at z = 6, that could have formed at z = 13.5, may prove to be those "hard to explain in lambda-CDM".

I will reiterate:

...even if the entire galaxy collapsed at z = 13.5, you still haven't shown that it's inconsistent with the standard model, nor have you cited any references that suggest a theoretical inconsistency.

You can't just wave your hands and say that it seems like it wouldn't work. You have to actually show it.


Baryonic DM resolves the galactic rotation curves, binds galactic clusters and lenses distant quasars. In order to resolve the problems with large-scale structure you need "non-pressurized" non-baryonic DM with properties chosen heuristically to make it fit. It is this hypothesis that I will question until DM is discovered in a laboratory.

Baryonic dark matter is ruled out by the MACHO results (a paper I'll probably link in my "Classic papers" post) and nucleosynthesis. The "non-pressurized" aspect follows directly from the need to be weakly-interacting (so as not to produce much light) and is not derived originally from LSS data. The only thing that was derived from LSS data was the "cold" part. We find that the universe looks entirely wrong if we assume the dark matter to be hot.


That has not yet happened and not for want of trying!

I hope you do understand that the very thing that makes it dark is that which makes it hard to detect.


I have, you will find a good resource of downloadable movies here. Notice that in the second and fifth movies that at z = 13.5 not much has happened.

The halos collapsing at z=13.5 would likely be very small and this simulation may not have the resolution to see them. It is standard CDM lore that reionization may have been caused by star formation at z ~ 17, so I don't think there are any theoretical problems there.


As you will have seen from my several posts on the subject the timescale in the standard Einstein-de Sitter model is too short for structure to form, even with non-baryonic DM. The hypothetical DE provides not only the acceleration necessary to fit the distant SN Ia data but also to stretch out these early time scales.

It does change the ages, but you certainly haven't shown that its required for the growth of structure. CDM theorists were having no trouble explaining LSS prior to 1998.


That depends on the physical properties of DE: quintessence? leaky branes? cosmological constant? etc. etc.? These properties have been heuristically chosen to make the model fit.

It sounds to me like you're just saying that the models are being consistent with the observations. God forbid! The simple fact that the universe is accelerating now implies a negative equation of state, which itself implies that dark energy was negligible at early times. What I'm saying is that you'd have to add extra parameters to your model (that changed the equation of state dramatically with time) to make it a contributor at nucelosynthesis.


The theory may be found for free on the physics ArXiv as well. It does fit cosmological constraints without invoking DE or exotic DM.

Given how little understanding of cosmology you've displayed in this thread, I find it hard to believe that your model correctly fits the data, and given how often you post links to your paper, I'm becoming increasingly convinced that you're a crank. If you're so sure that your theory is right, I suggest you try to hawk it in academic circles, where there are more people who can make a real critique.


I agree, but why choose an unknown exotic form of DM when ordinary baryonic matter (now mainly in the form of IMBH's?) may do the job just as well?

The primordial black hole solution is one possible explanation, but a large fraction of parameter space has already been ruled. Also, it's hard to form that many black holes in the early universe.
 
  • #32
SpaceTiger
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turbo-1 said:
Obviously, not ANY guesses! :uhh: I've been down that road...

Ok, how about we say, "guesses that aren't inconsistent with other observations"?
 
  • #33
Garth
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SpaceTiger said:
I will reiterate:
...even if the entire galaxy collapsed at z = 13.5, you still haven't shown that it's inconsistent with the standard model, nor have you cited any references that suggest a theoretical inconsistency.
You can't just wave your hands and say that it seems like it wouldn't work. You have to actually show it.
We have been discussing a paper about the observation of mature stars in galaxies of mass 1.3-3.8x1010Msolar at around z = 6, which may have formed as early as z = 13.5. As there seems to be a problem getting stars in dwarf galaxies to form beyond z = 7 because of re-ionization issues; see Formation of Dwarf Galaxies during the Cosmic Reionization, is not the onus is on the standard model to show that it is consistent with the observation of such galaxies and their stars?
Baryonic dark matter is ruled out by the MACHO results (a paper I'll probably link in my "Classic papers" post) and nucleosynthesis. The "non-pressurized" aspect follows directly from the need to be weakly-interacting (so as not to produce much light) and is not derived originally from LSS data. The only thing that was derived from LSS data was the "cold" part. We find that the universe looks entirely wrong if we assume the dark matter to be hot.
'Weakly-interacting' is a sufficent but not necessary condition for 'dark'. Interacting forms of matter can form dark objects, Jupiters or bricks for example - or my favourite IMBH's.
I hope you do understand that the very thing that makes it dark is that which makes it hard to detect.
Not necessarily; put an astronomically dark object into a laboratory - a comet nucleus of 5% albedo for example and it becomes very easy to detect!
The halos collapsing at z=13.5 would likely be very small and this simulation may not have the resolution to see them. It is standard CDM lore that reionization may have been caused by star formation at z ~ 17, so I don't think there are any theoretical problems there.
It uses 1000,000,000 particles! Masses of 106Msolar form at z ~ 17, we are talking about ~1010Msolar.
It does change the ages, but you certainly haven't shown that its required for the growth of structure. CDM theorists were having no trouble explaining LSS prior to 1998.
Structure takes time.
It sounds to me like you're just saying that the models are being consistent with the observations. God forbid! The simple fact that the universe is accelerating now implies a negative equation of state, which itself implies that dark energy was negligible at early times. What I'm saying is that you'd have to add extra parameters to your model (that changed the equation of state dramatically with time) to make it a contributor at nucelosynthesis.
So we know what DE is do we, and therefore know its equation of state? Or do we simply know what equation of state we require and therefore what kind of DE we have to invoke to make the model concordant?
Given how little understanding of cosmology you've displayed in this thread, I find it hard to believe that your model correctly fits the data, and given how often you post links to your paper, I'm becoming increasingly convinced that you're a crank. If you're so sure that your theory is right, I suggest you try to hawk it in academic circles, where there are more people who can make a real critique.
Forgive me for promoting my theory, but when you say: "There aren't yet any competing theories that can say the same." and there clearly is at least one I feel bound to contradict you. Perhaps I am a crank, (actually I prefer the term 'maverick'!), on the other hand cranks are not published in GRG, and the theory is discussed in academic circles with now 49 other author citations in peer reviewed journals. Its main plus point is that it is falsifiable and being tested at the moment as the Gravity Probe B experiment comes to its conclusion.
The primordial black hole solution is one possible explanation, but a large fraction of parameter space has already been ruled. Also, it's hard to form that many black holes in the early universe.
Agreed - a task in hand!

Garth
 
  • #34
turbo
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SpaceTiger said:
Ok, how about we say, "guesses that aren't inconsistent with other observations"?
If you are willing to consider that "empty" space is a transmissive medium and that the field of the quantum vacuum can exhibit densification and polarization like any other field, I can deliver "guesses" that are not only not consistent with observation, but make sense of some very perplexing problems.

If we insist that the quantum vacuum is exactly equivalent to "empty" space and that all EM of all wavelengths propagates through it with NO interaction, we will never manage to come up with a cosmological model that can allow the reconciliation of gravity with the three fundamental forces. The BB theory is founded on this "no interaction" concept. You may be interested in knowing that Edwin Hubble was not comfortable with this concept, or the "cosmological expansion" that was posited based on his observations.

I am in my mid-50s, and am trying to build a retirement fund, so I don't have the time or resources to go back to school and provide mathematical quantification for this model. You'll be able to dismiss me as a crank at for at least the next 10-12 years - tons of fun! I am an amateur astronomer and an ABO -certified optician, and initially started studying the quantum vacuum in order to explore a classical optical model for "gravitational" lensing that does not rely on the concept that massless photons follow geodesics in curved space-time.
 
  • #35
SpaceTiger
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Garth said:
We have been discussing a paper about the observation of mature stars in galaxies of mass 1.3-3.8x1010Msolar at around z = 6, which may have formed as early as z = 13.5. As there seems to be a problem getting stars in dwarf galaxies to form beyond z = 7 because of re-ionization issues; see Formation of Dwarf Galaxies during the Cosmic Reionization

It's suggesting that a z = 7 reionization yields a UV background that suppresses star formation at z < 7, which is exactly the opposite of what you're trying to show...

Also, the first two sentences of the paper:

In the context of cold dark matter (CDM) cosmology,
the first generation of objects should have the mass of
∼ 106M⊙ and form at redshifts of 20 . z . 50 (Tegmark
et al. 1997; Fuller & Couchman 2000). At later epochs, the
first objects are assembled into larger systems in a hierarchical
fashion to form dwarf or normal galaxies.

...which is of course exactly what I was saying earlier in the argument. Combine the above with the fact that the observations are selectively finding the brightest objects and thus sampling the high-mass tail of the galaxy distribution and I would say that the standard model is pretty safe.


'Weakly-interacting' is a sufficent but not necessary condition for 'dark'. Interacting forms of matter can form dark objects, Jupiters or bricks for example - or my favourite IMBH's.

I was assuming a particle source of dark matter (which seems much more probable given the observations), but I can assure you that "bricks" would not be pressurized either.


Not necessarily; put an astronomically dark object into a laboratory - a comet nucleus of 5% albedo for example and it becomes very easy to detect! It uses 1000,000,000 particles!

That requires you to actually find it first! If you concentrate the dark matter into massive objects, then they also become very sparse and the chances of one passing close enought to detect becomes very small. If you're looking for another calculation to do, try calculating the number of dark matter objects that would pass through the solar system in a decade as a function of their mass given the current observational data.


Masses of 106Msolar form at z ~ 17, we are talking about ~1010Msolar.

Again, I'm going to refer you to the hierarchical model of growth. All of the stars in the galaxy do not have to be formed at the time of the galaxy itself. The observational limits are on the ages of the stars.


So we know what DE is do we, and therefore know its equation of state? Or do we simply know what equation of state we require and therefore what kind of DE we have to invoke to make the model concordant?

We were talking in the context of dark energy models, so I naturally assumed that we would be discussing ones that fit the data. :rolleyes:


Forgive me for promoting my theory, but when you say: "There aren't yet any competing theories that can say the same." and there clearly is at least one I feel bound to contradict you.

What I actually said was:

I don't disagree that dark matter and dark energy are unsettling, but they fit the data and have even made successful predictions. There aren't yet any competing theories that can say the same.

I'll grant you the possibility that your theory fits the data (though I doubt it), but what successful predictions have you made?


Perhaps I am a crank, (actually I prefer the term 'maverick'!), on the other hand cranks are not published in GRG

Actually, I'll bet they do


and the theory is discussed in academic circles with now 49 other author citations in peer reviewed journals. Its main plus point is that it is falsifiable and being tested at the moment as the Gravity Probe B experiment comes to its conclusion.

I look forward to the results.
 

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