Discovery Challenges Galaxy Formation Theories

[Reality Check]

Here's a new paper relevant to this thread: The Current Status of Galaxy Formation. Towards the end of the paper is a substantial and interesting list of current problems with theory versus observations.

This new paper Evolution of Massive Galaxy Structural Properties and Sizes via Star Formation In the GOODS NICMOS Survey discusses one of the important problems which is how galaxies got so much larger since z = 2 (3 to 5 times in radius). It argues that star formation cannot be the answer. Various star formation scenarios analyzed can account for only a small part of the growth. Also, there don't appear to be enough major mergers to account for the growth. (Maybe they haven't really grown?)

Two very interesting papers though your summary of the second paper is not quite correct. That paper presents evidence that star formation cannot be the full answer for the observed increase in effective radius for massive galaxies. They then suggest that mergers may supply the rest of the answer.

We conclude that due to the lack of sufficient size growth and Sérsic evolution by star formation and stellar migration other mechanisms must contribute a large proportion to account for the observed structural evolution from z > 1 to the present day. Recent studies by Bluck et al. (2011) have found that minor and major mergers have a large influence on the size of massive galaxies possibly contributing the remaining 80% of size growth needed to explain the observed trends.

[Reality Check]

antoniseb. There might be one. The effect proposed by Catherine Braiding in star formation cannot be excluded from being used for more extended sources...galaxies.
SEE:http://arxiv.org/pdf/1110.2168v1.pdf
SEE:http://arxiv.org/abs/1109.1370

pete

Hi pete - I suspect that the Hall effect in the formation of stars may not be applicable to galaxies. This effect dominates at intermediate densities during star formaiton. At low densities, ambipolar diffusion dominates. Galaxies have relatively low densities and during their formation are are mostly neutral hydrogen (it is the formation of stars in the galaxies that ionize hydrogen).

[Cougar]

I can't pretend to truly understand it, but the gist seems to be that no matter how you juggle the pieces they don't fit well.

I guess that's one way of looking at it. That recent paper, The Current Status of Galaxy Formation by Joe Silk and Gary Mamon, submitted on 12 Jul 2012, was quite the literature review on the topic. I thought the gist was that there's still a lot we don't know about early structure formation and evolution. A field ripe for discovery.

[TooMany]

Two very interesting papers though your summary of the second paper is not quite correct. That paper presents evidence that star formation cannot be the full answer for the observed increase in effective radius for massive galaxies. They then suggest that mergers may supply the rest of the answer.

Maybe but there are issues. Here's one of the merger assumptions listed on page 11 of the paper:

While the gas settles into disks, major mergers of galaxies cause disks to transform into ellipticals, and after subsequent disk build-up, the merger remnant is identified to a bulge inside a spiral galaxy.
The bulge can also be built-up by repeated minor mergers, as well as starbursts and secular evolution of the disk.

So in order to explain disk galaxies, major mergers occur first building an elliptical which becomes the core of a neat spiral no longer damaged by major mergers because there are only minor mergers subsequently? Well maybe, but on the other hand, they also attribute very massive galaxies (presumably ellipticals) to major mergers too. How do they explain disk galaxies without bulges?

Here's another assumption in the same list:

Satellite galaxies trajectories are assumed to be those of the subhalos they belong to, and when they
are no longer resolved in the cosmological simulation, or if one is only using a halo merger tree, the
galaxies are merged with the central galaxy on a dynamical friction time.

LCDM theory predicates large numbers of satellite galaxies (some much larger than any observed) in a random distribution. There are several difficulties with that. One is that our galaxy has no such distribution of satellites (nor does M31). The few satellites that we have orbit in a plane roughly perpendicular to the disk. If the disk was built up by mergers of such satellites over time, it's hard to explain the thin disk. If the satellites are gone due to mergers, that needs explanation. How is it that so few survive? Shouldn't there be some in more distant orbits which cannot fall in the allowed time?

That's the sort of thing I'm getting at with the puzzle parts not fitting. It's hard to invent a hypothesis for this growth that is consistent with all of the galaxies and observations. Perhaps these merger hypotheses can be conjectured without substantiation because we are as yet unable to simulate the details?

In case you missed it, the paper ends with a long list of problems (15) introduced by this sentence:

Here is a summary of some of the key reasons why CDM does not yet provide a robust explanation of the observations: we list below several examples that represent challenges for theorists.

This is a bit of an understatement since many of the problems listed indicate that the LCDM model contradicts observation. Then in the final paragraph the hope is presented that some current misunderstanding will eventually solve the problems, presumably in the context of LCDM.

We can only wait and see. In the meantime since astronomers have no alternative theory, they will continue to approach the puzzle by trying to understand why observations don't match theory and look for explanations that bring observations back into line with existing theory. This approach is evident in papers recently published that try to explain the lack of cusps and the BTF relation. Theorist are looking to explain away the apparent problems with the theory. They are not considering alternative explanations, because they are deeply committed to the theory they have (undoubtedly for some good reasons). One way to put it is that thinking is still within the box. Perhaps out of the box thinking will become necessary if more serious difficulties arise.

[Gigabyte]

Since we can observe many different kinds of galaxies, shouldn't there be multiple theories to explain the different kinds?

In keeping with the topic, I just found the following article about an article from Nature. (I wish I had found it years ago now)

Astrophysicists have long been trying to understand the way in which these two types of galaxies are formed. Some experts say this question is the primary challenge facing modern cosmological researchers today, as galaxies formation is “an essential stage in the cosmological process that leads to the formation of life.” Until now, the standard model explained galaxy formations by spherical gas infall into a central disk, followed by mergers between disks. Stars were assumed to form slowly within the gaseous disks, which converted into globes as they merged. In such a “merger” the colliding gas clouds produce a big burst of new stars at a rate of hundreds of solar masses per year.


Recent astronomical observations, however, put the accepted theory to question as new data was collected using advanced telescopes, which allowed scientists to examine the galaxies as they were about three billion years after the Big Bang. “The large galaxies, as they appear in this early stage, indeed created stars at a very rapid rate, but this does not appear to be at all a result of galactic mergers” - said Avishai Dekel, professor of theoretical physics at the Racah Institute of Physics in the Hebrew University. The observations led researchers to ask the natural question – “How is it that these galaxies were able to form stars so quickly and in large quantities at such an early stage without massive galactic mergers?”

http://thefutureofthings.com/news/65...-proposed.html

Now it may be possible the author of that piece is some kind of an idiot, but he does write, "Recent astronomical observations, however, put the accepted theory to question as new data was collected using advanced telescopes, which allowed scientists to examine the galaxies as they were about three billion years after the Big Bang."

I'm going to use that to feel all vindicated again.

[TooMany]

Since we can observe many different kinds of galaxies, shouldn't there be multiple theories to explain the different kinds?

In keeping with the topic, I just found the following article about an article from Nature. (I wish I had found it years ago now)


http://thefutureofthings.com/news/65...-proposed.html

Now it may be possible the author of that piece is some kind of an idiot, but he does write, "Recent astronomical observations, however, put the accepted theory to question as new data was collected using advanced telescopes, which allowed scientists to examine the galaxies as they were about three billion years after the Big Bang."

I'm going to use that to feel all vindicated again.

One of the researchers mentioned (Avishai Dekel) goes on to propose a growth mechanism that is not based on mergers but rather cosmic cold filaments of gas (and DM?) that galaxies seem to form along. The galaxies grow as gas from the filaments falls through the halo and clumps into molecular clouds. I think these would be the same filaments seen in structure formation simulations. This gets interesting because then you have to ask what is the behavior of filaments which presumably contain both baryonic and collisionless non baryonic matter. If somehow a filament of both baryonic and DM were falling into a galaxy, one might expect the baryonic matter to pile up into clumps while the non-baryonic matter sails right through.

The paper behind the article could be this one:

Formation of Massive Galaxies at High Redshift: Cold Streams, Clumpy Disks and Compact Spheroids

There are some papers published lately in which it is suspected that the merger theory is wrong. It seems fair to say that it's all up in the air at present.

[Cougar]

Since we can observe many different kinds of galaxies, shouldn't there be multiple theories to explain the different kinds?

Well, no. You'd want a single theory to be able to explain them all. The general theory of relativity and the standard model of particle physics are currently doing a pretty good job at the overall explanation. Apparently many scientists are not even satisfied with that , and they think there ought to be some kind of unification of the two, the realization of which has so far eluded them.

[Reality Check]

Maybe but there are issues. Here's one of the merger assumptions listed on page 11 of the paper:

Wrong paper. The second paper whose summary you do not quite get right is: Evolution of Massive Galaxy Structural Properties and Sizes via Star Formation In the GOODS NICMOS Survey.

So in order to explain disk galaxies, major mergers occur ...

Yes - that is an ingredient of the galaxy formation simulations.

Here's another assumption in the same list:

And another ingredient of the galaxy formation simulations.

So what?
You need to include some kind of physics in computer simulations.

You seem to be concentrating on a rather trivial aspect of science - there are nearly always "puzzle parts not fitting" in scientific models.
Scientists know this which is why they are always trying to improve models.

It's hard to invent a hypothesis for this growth that is consistent with all of the galaxies and observations.

In fact it is easy to explain the growth of galaxies as in the second paper: stellar evolution + migration + mergers = growth in effective radius.

In case you missed it, the paper ends with a long list of problems (15) introduced by this sentence:

In case you missed it, this long list of problems (15) includes solutions for many of the probelms.

The LCDM model does have several problems on small scales. That has not much impact on the validity of the LCDM model because it works at larger scales as the paper's introduction states.
The authors think that the small scale problems will be resolved with better physics and models (see page 2):

However, the naıve assumption that stellar mass follows halo mass, leads to too many small galaxies, too many big galaxies in the nearby universe, too few massive galaxies at high redshift, and too
many baryons within the galaxy halos. In addition there are structural problems: for example, massive galaxies with thin disks and/or without bulges are missing, and the concentration and cuspiness of cold
dark matter is found to be excessive in barred galaxies and in dwarfs. The resolution to all of these difficulties must lie in feedback. There are various flavours of feedback that span the range of processes
including reionisation at very high redshift, supernova (SN) explosions, tidal stripping and input from active galactic nuclei. All of these effects no doubt have a role, but we shall see that what is missing
is a robust theory of star formation as well as adequate numerical resolution to properly model the interactions between baryons, dynamics and dark matter.

So we can only wait and see: Are the problems at small scales a result of incorrect physics in the computer simulations? Or are the properrties of DM even stranger than we think? Or it is something else?

[Gigabyte]

Meanwhile

http://www.msnbc.msn.com/id/48229023.../#.UAdnlmGe6dw

[Tensor]

Meanwhile

http://www.msnbc.msn.com/id/48229023.../#.UAdnlmGe6dw

LOL, I've been waiting for you to post this since this afternoon, when I saw it in various different outlets. The problem is the articles don't include the important stuff in the actual paper. You know, like the merging galaxy that causes the formation of the spiral structures has to be of a certain size and orientation, or the spiral structures won't form. That the spiral structures, unlike nearby spirals, are unstable and are short term features ( < 100 Myr). That the spiral structures can't form, unless the large galaxy is of a certain minimum size. Or that they have to be oriented to near face-on and be observed within the short time frame of for us to see them. I figured you would get all excited about it, but you wouldn't bother running down the paper to actually read it to find all the caveats that aren't usually listed in "Science by Popular Science article". Go over to "Fun Papers in Arxiv", the link to the actual paper is the first paper listed.

[Gigabyte]

The problem is the articles don't include the important stuff in the actual paper.

It's not a problem, because they quoted the lead researcher.

"The fact that this galaxy exists is astounding," study lead author David Law, of the University of Toronto, said in a statement. "Current wisdom holds that such ‘grand-design’ spiral galaxies simply didn’t exist at such an early time in the history of the universe."

[Tensor]

It's not a problem, because they quoted the lead researcher.

"The fact that this galaxy exists is astounding," study lead author David Law, of the University of Toronto, said in a statement. "Current wisdom holds that such ‘grand-design’ spiral galaxies simply didn’t exist at such an early time in the history of the universe."

Like I said, the paper explains why the spiral structures are not permanent, so the galaxy is not really a "grand design" spiral at such an early time in the history of the universe. The lead researcher had all that put in the paper. Science by quote doesn't work too well, as the quotes in an article and the actual science in the paper may not always match. It also has a tendency to make people feel like they are in over their head, when confronted with the actual science.

[Cougar]

It's not a problem, because they quoted the lead researcher.

You seem to be quote mining, Gigabyte. Your linked MSNBC article (an outfit not known for scientific rigor) also says:

The Hubble and Keck observations also revealed a companion dwarf galaxy residing near BX442. The scientists think the gravitational interaction between the two galaxies may be creating BX442's spiral shape, possibly explaining how it became so different than its galactic contemporaries.

Did you have a particular comment about this finding?

[TooMany]

You seem to be quote mining, Gigabyte. Your linked MSNBC article (an outfit not known for scientific rigor) also says:

The Hubble and Keck observations also revealed a companion dwarf galaxy residing near BX442. The scientists think the gravitational interaction between the two galaxies may be creating BX442's spiral shape, possibly explaining how it became so different than its galactic contemporaries.

Did you have a particular comment about this finding?

Well, I've just got to mine my favorite quote from the abstract:

Alternatively, current instrumentation may simply not be sensitive enough to detect spiral structures comparable to those in the modern Universe.

I'm betting that this is the real answer. There are plenty of spirals, they just don't look like them because the structures are too dim to detect, except in the very brightest galaxies. Unfortunately it's going to be many years before this hypothesis can be proven right or wrong. The JWST should settle the issue.

I might add that the OPs are also selective among the possibilities proposed, choosing those that they favor.

[Tensor]

Well, I've just got to mine my favorite quote from the abstract:

Alternatively, current instrumentation may simply not be sensitive enough to detect spiral structures comparable to those in the modern Universe.

But somehow it's sensitive enough to detect this one, but not other brighter ones? Good point.

I'm betting that this is the real answer. There are plenty of spirals, they just don't look like them because the structures are too dim to detect, except in the very brightest galaxies.

There are brighter galaxies at that z, than the one under discussion, but our instruments are only sensitive enough to detect the spiral structure in this one, not the brighter ones? Another good point.

Unfortunately it's going to be many years before this hypothesis can be proven right or wrong.

No it's not. At least not at this z. Unless you have a good explanation for why other, brighter galaxies, at this z, don't exhibit spiral structures, when the model in this paper explains it and is consistent with observations.

The JWST should settle the issue.

It may at greater z.

I might add that the OPs are also selective among the possibilities proposed, choosing those that they favor.

Actually, it's not that we favor them so much, as we're trying to provide the possibilities the others ignore or don't even know about because they don't read the actual papers.

[TooMany]

The author's of the paper said:

Alternatively, current instrumentation may simply not be sensitive enough to detect spiral structures comparable to those in the modern Universe.

I said:

[I'm betting] there are plenty of spirals, they just don't look like them because the structures are too dim to detect, except in the very brightest galaxies.

But somehow it's sensitive enough to detect this one, but not other brighter ones? Good point.
There are brighter galaxies at that z, than the one under discussion, but our instruments are only sensitive enough to detect the spiral structure in this one, not the brighter ones? Another good point.

You need to deliberately misinterpret what I said (in an illogical way) to make some point? And add some sarcasm to boot?

Actually, it's not that we favor them so much, as we're trying to provide the possibilities the others ignore or don't even know about because they don't read the actual papers.

What you pointed out, about the satellite galaxy possibly shaping the arms of this spiral, is stated in the news story sited by Gigabyte and in the paper's abstract. The possibility that I quoted above is not in the news story, but it is in the paper's abstract.

[Gigabyte]

Sarcasm is against the rules. I just found this out recently.

[Nereid]

Of some relevance, this, hot off the arXiv press: A new scaling relation for HII regions in spiral galaxies: unveiling the true nature of the mass-metallicity relation (F. F. Rosales-Ortega et al.):

We demonstrate the existence of a -local- relation between galaxy surface mass density, gas metallicity, and star-formation rate density using spatially-resolved optical spectroscopy of HII regions in the local Universe. One of the projections of this distribution, -the local mass-metallicity relation- extends over three orders of magnitude in galaxy mass density and a factor of eight in gas metallicity. We explain the new relation as the combined effect of the differential radial distributions of mass and metallicity in the discs of galaxies, and a selective star-formation efficiency. We use this local relation to reproduce -with remarkable agreement- the total mass-metallicity relation seen in galaxies, and conclude that the latter is a scale-up integrated effect of a local relation, supporting the inside-out growth and downsizing scenarios of galaxy evolution.

(my bold)