Do galaxies age 'gracefully'?


This article in Space.com, Nature vs. Nurture in the Cosmos, there seems to be evidence of a gradual evolution of galaxies. It says: Now, if this analysis of galaxy star formation is correct (see pix in article for examples), where a galaxy at 7 million light years has many blue stars, while one at 33 million light years has only a peripheral remnant, and at 62 million light years nearly no blue stars, then it seems there is a natural progressions tied into time and distance for galaxy evolution.

The first ATM question is: Can a galaxy evolve to full maturity in such a short time, of only about 50 to 60 million years?

The second question is: What are we actually observing? Do we actually know this analysis of galaxy evolution based on blue stars observation is correct?

Consider this possibility: (1) that beyond a certain distance, blue stars are no longer observable, if their light shift turns towards the red; and (2) if it takes only about 60 million years for a galaxy to reach full maturity, shouldn't there be some evidence of 'star formation' beyond the 62 million light years 'horizon'? Or (3) if there are blue stars observable beyond 62+ million light years horizon, then what does it mean in terms of galaxy evolution, if these galaxies are creating new stars at any time scale? What about billions of light years away? In fact, shouldn't it all be in reverse, that older (farther away, farther back in time) galaxies show more star formations, if the universe is expanding from a Big Bang (so called) origin?

I propose, from #3, that the above article has either not given us enough information to come to a necessary conclusion about galaxy evolution, or because older (farther away) galaxies are not showing more star formations, that the observation is flawed. Furthermore, is about 60 million years enough time to complete a full cycle of galaxy evolution from youngster to old age, gracefully?

What we are actually seeing, in effect, is that over great distances the blue stars simply are not observable, not even at the ultraviolet wavelength. The above hypothesis is therefore flawed because of an observational limit, that older blue stars are not observable. In fact, we should be seeing more blue stars at billions of light years, in my opinion, if galaxies formation was more common then, closer to the Big Bang 'origin' of the universe.

What do you think? Here's the conundrum: Looking back farther in time into the early universe, we should be seeing more star formation, not less! ATM here?

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We see more starburst galaxies at high z than low z. That is not necessarily revealing, but useful.

Thanatos, the conundrum here is that we should see a progression of star formation in reverse, where older galaxies (father away) should show more star formation (more blue stars), with closer galaxies (more recent) maturing into less blue stars, if the article's premise is to be take face value. However, that is not how it was presented, where the newer galaxies with more star formations were more recent (closer to us) while the older more mature galaxies were further away (older) had fewer blue stars. I think this presents a problem, because if age of the universe is a factor, it should be in reverse order, as you point out. There are more starburst (new stars) galaxies at high Z than low z. The only solution to this, if there is a solution here, is that blue star formation is not indicative of the age of any given galaxy. In fact, it may be indicative of our inability to observe blue light stars over great distances instead. Isn't this the problem?

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1) full maturity in 50 Myr?

doubt it. While that would get out alot of the really blue O and B stars, I think the A stars can last longer. If I remember right, you prolly want upwards of a billion to get to maturity. Even then, there will still be alot of white and yellow.

2) I think you are observing the summed color spectra of all the galaxy. The blue drains out first. As to how much is correct, 100 years of observation of billion year timescale effects means there is still alot of if and maybe.

3) I know blue galaxies are common in the hubble deep field, so there are some waaaay out there. I also know that there are effects that can make galaxies very blue. Collision seems to be one of the big ones. I think that the current thought is that galaxies start mostly spiral, then collide with their neighbors, which tends to make them very blue for a while, and also tends to change the spiral to an elliptical, then they end up being an evolved mature elliptical.

Why is this in ATM? It looks like reasonable questions and answers stuff.

Let's get the chronology straight, at least as I understand it according to the most up to date theory.

The galaxies have been around for some billions of years. We see the nearby ones as they were very recently, and the more distant ones as they were in earlier stages of their evolution.

Star formation rates were generally higher in the earliest stages, and massive, brilliant blue stars of types O and B are believed to have been more abundant. Thus I would expect to see more blue light in the most distant ones. It will be redshifted, but the spectral lines will identify it as intrinsically blue. Redshift alone should not make the blue light unobservable.

If the opening round of star formation had been all there was, there would be no remaining blue stars to be seen in nearby galaxies. The fact that some galaxies, including our own, have an impressive sprinkling of them indicates that episodes of star formation have occurred in recent times. Collisions and mergers can provide the necessary perturbations to start new episodes in previously quiescent interstellar gas and dust.

Other galaxies, which have insufficient remaining gas for such star formation, will have only "later" type main sequence stars, red giants, and the dim or dark remnants of the primordial blue stars. These are the ones that are described as old and red.

I don't think the nearby blue galaxies are younger overall. They just have a greater abundance of star-forming capability. I think the SPACE.com writer used some poor choices of words. I am skeptical when a writer uses gussied up figurative language such as "sexy" in such a context. I would rather hear more from Mr. Martin directly concerning the intermediate stages of galactic evolution.

Yes, and that is exactly what we see, as the article you linked to indicates ...
The cosmic star formation rate is seen to peak about a redshift of 3, about 11,500,000,000 years ago, when the universe was about 2,200,000,000 years old. It has fallen off by about a factor of 10 since then. See, for instance, Hopkins & Beacom, 2006.

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The conclusion that all observational evidence is consistent with the standard model framework is simply not true.


One of the outstanding features of the ‘early’ universe is that galaxies out to redshift 7 appear to have normal stellar populations (Richard S. Ellis, Caltech, 2004).

Using data obtained with the Frederick C. Gillett Gemini North Telescope on Mauna Kea, Gemini Deep Deep Survey took the deepest spectra ever of very distant galaxies. The galaxy populations encountered look identical to local groups, with astoundingly no sign of evolution during this important era that was believed to be one of most significant change.

"It is quite obvious from the Gemini spectra that these are indeed very mature galaxies, and we are not seeing the effects of obscuring dust. Obviously there are some major aspects about the early lives of galaxies that we just don’t understand.” Said Patrick McCarthy (Observatories of the Carnegie Institution).

“Studying the chemical composition of the interstellar gas, we discovered that the galaxies in our survey are more metal-rich than expected." Sandra Savaglio (Johns Hopkins University).

Hold on, there’s more: Isobel Hook (see Hook et al, c2004), head of the UK Gemini Support Group, (Oxford University) is part of the Gemini Deep Deep Survey (GDDS) team whose objective is to capture the faintest galactic light ever detected. Three hundred galaxies were scrutinized. “These highly developed galaxies, whose star-forming youth is in fact long gone, just shouldn’t be there, but are," said Co-Principal Investigator Karl Glazebrook (Johns Hopkins University).

Others too have found that distant red galaxies in the Hubble Ultra Deep Field (Toft et al 2005) present morphological properties that suggest “complex stellar populations, consisting of both evolved populations that dominate the mass and the restframe optical light, and younger populations, which show up as patches of star formation in the restframe UV light; in many ways resembling the properties of normal local galaxies."

The supposition that the morphology of galaxies in the Hubble Deep Fields is very different in the past than in the present is not a confirmed observational fact, when redshift and surface brightness are taken into account (Buta & Block 2001, Thompson, R.I, 2000, Ellis 1997, Takamiya 1999).


Coldcreation

Short lived 'baby boom' star clusters last only a few dozen million years, per this Hubble article: http://hubblesite.org/newscenter/arc.../2007/05/full/

However, note these are very specific stars (per korjick), B stars that burn out quickly and not indicative of other globular clusters of A stars last much longer. Also, star clusters are not uniformly the same, since some of the may give 'star birthing' in several generations: http://hubblesite.org/newscenter/arc.../2007/18/full/ There's the dilemma, to find evidence for what we see in the very early universe at high Z~6 in the Z<~1 universe, much closer to home.

The way this OP article was written, with its illustrations of (reverse) order of star birthing and maturing from 7 MLY to 62 MLY gives one the impression that there should be (within a few dozen million years) a marked evolution from birthing to maturing galaxies. However, this is in reverse order, because we should be looking (from galaxies reference frame) as older galaxies (newer in their reference frame) being where the birthing is more pronounced, not more recently. The trouble with this idea (where it is ATM) is that if we do not find local evidence of such birthing and maturing, then how are we to interpret it in the very ancient (billions of light years) universal star formations, where they 'appear' to have been very much more active than today (by factor of 10?), since we do not see such activity here? (Except for when galaxies collide?) Either that, or something was truly fundamentally different billions of light years ago versus what the universe looks like today; or our instruments looking back 13 BLY make it 'look like' it was very different. The only problem with this (ATM) is that when they look back to 13 BLY, they find already fully formed galaxies.

Can the universe birth itself within a mere <~1 billion years? Or, as ColdCreation said: The idea is that what happened in the very early universe, some 13 Billion years ago, where fully formed galaxies already existed, should not be contrary to what is happening today, where new stars are birthing, if the universe is the same today as it was 13 billion years ago (where fully formed galaxies already existed). The problem (ATM) is that the order of birthing seems to be reversed, whereby older galaxies (newer from galaxy reference frame) show more mature star formations, and new galaxies (older from galaxy reference frame) show newer star formations. Shouldn't this actually show up in reverse (from galaxy frame reference)? It looks right from our frame reference, but wrong from galaxy frame reference, unless we find evidence in total reverse: Older galaxies have newer star formations (Z~<1) and newer galaxies (z<~1) have more mature stars.

Have we seen this? I searched, and all I found was references to 'distant star bursts': http://www.spaceref.com/news/viewpr.html?pid=12569 , which observed 12 BLY back (UK ATC), but no evidence that this (reverse order) had been observed. What are we missing here?

What Hornblower says makes sense, that type O and B stars were eliminated early on, but there should be some evidence of this happening now too. And if the evidence is found, then it means the universe is still evolving just as it was evolving 13 billion years ago, without any change whatsoever. In fact, to extrapolate back a bit, it may not have changed at all over its 13 BLY history (all we can see), except that our ability of observation has changed. In effect, the universe might even be much older than what we think (ATM). But to prove this idea, that the universe is the same now as it ever was, we need to find the correct progressions of type O and B stars within our local reference frame (reverse order for local galaxy reference frame), but which the OP article seems to contradict.

And that's the crux of the matter: we should be seeing star birthing from the galaxy reference frames, which is reverse of what we see from ours. Or as Tim Thompson's refered (abstract) says: Should we be seeing the same rate of star birthing in Z<~1 as much farther back in time, then there is no compelling argument for the early universe being different from the present one, barring any meaningful adjustments with 'normalization and analytical formalisms'. What are we actually observing, if we do not find evidence of greater star birthing in the time sequences of Z<~1 in reverse order (from galaxy reference frame) than what had been observed (from our reference frame)? Rather, it appears we find the opposite effect (from our reference frame) of more birthing closer in, rather than farther out. This begs the question (ATM) as to what is it we are seeing with our instruments at the blue light spectrum? Are our readings true, or are they obscured by space dust, or otherwise, to let us see blue star formations closer in (not farther out)?

Or, in effect, are our instruments not up to par at the blue light/ultraviolent range, because of all the space dust in between here and there? So what we get in merely a skewed picture, where older stars (in there reference frames) or galaxies appear younger to us? But that's opposite of what it should be!

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I cannot find anything in your long list which is inconsistent with big bang cosmology. How do you know, or on the basis of what physics do you argue, that galaxies cannot form rapidly in big bang cosmology? How, exactly does the presence of a few evolved galaxies in the early universe actually contradict big bang cosmology?

The references you cite are incomplete, and none are linked back to papers or abstracts. I cannot easily find where you are getting your quotes. Can you be more complete in providing references?

What about the paper I linked to before: On the Normalization of the Cosmic Star Formation History, Hopkins & Beacom, Astrophysical Journal 651(1): 142-154, November 2006. I specifically reference figure 1 (you can download the PDF from the arXiv link). This figure explicitly shows the rapid decline in star formation rate since redshift 3, and the increase in star formation rate prior to that, from about redshift 6.6 to redshift 3. Is this figure in error, and if so, why?

And what about this: Evidence for strong evolution of the cosmic star formation density at high redshifts, Mannucci, et al., Astronomy and Astrophysics 461(2): 423-431, January II 2007. They find that no galaxies with redshifts as high as ~7 are visible in the GOODS-south field, in deep HST/ACS & VLT/ISSAC images. The non-detection is significant. In the abstract they reach this conclusion: "Our non detection of galaxies at z ~7 provides clear evidence for a strong evolution of the luminosity function between z=6 and z=7, i.e. over a time interval of only ~170 Myr. Our constraints also provide evidence of a significant decline in the total star formation rate at z=7, which must be less than 40% of that at z=3 and 40-80% of that at z=6." Strong evolution of the star formation rate is consistent with the results reported by Hopkins & Beacom.

The example of only a few evolved galaxies at high redshift is not contrary to these results. They are also not contrary to big bang cosmology, until & unless you are able to enforce your implied conclusion that galaxies cannot evolve as quickly as observed by Mannucci, et al., or quickly enough to be massive at redshifts as high as 6-7.

I can't follow the point you are trying to make, especially what you mean by "reverse" order. And I don't know what this is supposed to mean: "It looks right from our frame reference, but wrong from galaxy frame reference ...". So let me ask a couple of questions to clear my own vision.

Without reference to "reverse" order, and keeping in mind that larger redshifts are farther back in time, what do you think the cosmic star formation rate should look like to us in the Milky Way, here & now, if big bang cosmology is valid? Is the above referenced figure 1 from Hopkins & Beacom consistent with the way you think it should look?

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I had those links in another computer.

Here you will find most, if not all, of the quotes from my previous post.



Distant Red Galaxies in the Hubble Ultra Deep Field (Toft et al) arXiv:astro-ph/0503454 v1 21 March 2005

Ellis, R.S., 2004 Seeing the Very First Galaxies

Gemini Observatory, Faintest Spectra Ever Raise Glaring Question: Why do Galaxies in the Young Universe Appear so Mature?

and/or http://www.gemini.edu/project/announ...ss/2004-1.html

and/or Why do Galaxies in the Young Universe Appear so Mature?


Massive Distant Galaxy Calls Theory into Question

The Metallicity of 0.5 < z < 1 Field Galaxies




PS. I'll be back to respond to the rest of your post later.


Coldcreation

The time line of new blue stars in distant galaxies shows (per OP article) a time line going from more recent to older (7 MLY to 62 MLY) where blue stars progressively disappear. My term "reverse order" means that from the perspective of the light coming to us from the galaxies (light from their reference frames) should show newer blue stars formation (within the galaxies) happening in older (farther away) galaxies, and progressively disappear in newer (closer in) galaxies. Try to visualize this, because it is a relativistic phenomenon, by putting yourself in the point of view 'as if' you were looking at this from the other direction, that of the stars sending light towards us.

About your other question, "...what do you think the cosmic star formation rate should look like to us in the Milky Way, here & now, if big bang cosmology is valid?" I am not sure how to answer that, in part because I don't know if any sequence of star formation in our own galaxy has any identifiable pattern to work with. If the galaxy formed at some period of time, one would assume the stars within it evolved within a relatively short time to gather together into a galaxy around a central gravity 'black hole'. If I were observing this from a distant vantage point way beyond our galaxy, perhaps some pattern vis-a-vis other nearby galaxies (in line of sight) could show the pattern of blue star formation over time (distance), but I don't know if that answers you question. My opinion is that within a galaxy, no such progression is visible. Once an aggregate of stars forms into a galaxy, it is now its own internal phenomenon. The difference between this, one galaxy, and the star formation development from multiple galaxies (line of sight) is that the latter may show a progression with time of blue star formation. I think this is what the OP article was trying to show, but it did it in "reverse" given how the time line was presented. Can you see that? That's the main issue.

I can't do more now, must run out the door, but will study this some more and get back if find new stuff. I also have to read Coldcreation's links before going deeper.

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The author showed a blue galaxy at 7 million light years and a red galaxy at 62 million. She just as easily could have shown a blue one that is farther away. From that, along with her loose use of young and old as if she thinks they apply to the entire galaxy, you appear to have made a great-leap inference of the evolutionary time lines of those galaxies. Beyond that, I cannot follow your line of thought. Your expressions "older (farther away) galaxies" and "newer (closer) galaxies" make no sense to me. You appear to be inferring things that the author never said and never quoted anyone else as saying.

For all we know, both galaxies may be over 10 billion years old, and for whatever reason the red one has long since exhausted its supply of gas while the blue one has not. I see nothing in the article which implies otherwise. The 55 million year difference in the lookback times is a twinkling in comparison.

From this article and others on similar topics, I would guess that the red one is the result of past mergers in which the interactions accelerated the star-forming process and in the process exhausted the supply of gas. Computer simulations indicate that such mergers also scramble the original spirals and yield a large elliptical galaxy. Given enough time, the blue components of the other one will disappear and leave it similarly red. If it does not merge with another large galaxy I would expect it to remain a disk rather than become an elliptical blob.

Yes, this is exactly right. If she had shown the reverse order I would not have questioned it. Oversight on her part? Or is this simply 'not there' that in the time progression of an (expanding) universe the opposite does not exist? Or possibity that we are simply unable to register such blue stars further out? These are the unresolved questions.

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In terms of star colors, that is exactly what we should, and actually do see. But that's because our ability to see red stars falls off rapidly with distance. The red stars are invisible in the older galaxies, we can see only the blue stars, because they are hotter & brighter, and their light therefore carries over larger distance. So if you look only at the star colors, you will get a very skewed picture of the evolution of galaxies, because most stars are too red to see. Blue stars do not mean young galaxies, they mean young stars. Star formation is episodic, so that a very old galaxy could easily undergo a burst of star formation, pump up its blue star population, and make you think it is young when it is really very old.

It is better to look at the global star formation rate as a function of time (redshift). That's why I linked to the Hopkins & Beacom paper where you can see the history you expect to see. At high redshift the star formation rate is low, simply because things haven't got started yet, except in a few places. But the star formation rate goes up dramatically as star formation really gets going, peaking about redshift 3 (about 11.5 billion years ago). Since then the global star formation rate has fallen off by about a factor of 10.

Aside from the selection effects involving star color, there is also the small numbers problem. You cannot hope to learn anything at all about star formation in the universe by looking only at 2 or 3 galaxies, as there are always exceptions. You need to look at thousands of galaxies, more if you can. That's how the star formation history studies work. So, even though we know that the global star formation rate is low at high redshifts, that does not exclude the local star formation rate from being quite high in some places (i.e, HUDF-JD2, if it is really as far as redshift 6.5; Chary, et al., 2007 argue that it is actually much closer, about redshift 2; this also serves to show the difficulty of determing the redshift for distant galaxies).

Consider the galaxies featured in the OP story. The "blue" galaxy at 7 million light years is NGC 300. But is it "blue", or do we only see blue stars slectively? And remember that the GALEX instrument looks only in UV, so it would not efficiently see red stars even if they were nearby. See Butler, Martinez-Delgado & Brandner, 2004. They conclude that "The main disk stellar population is predominantly old, consisting of red giant branch (RGB) and asymptotic giant branch (AGB) stars ..." and "Taken at face value, this finding would agree with the Davidge report of suppressed star formation there during the past 10⁹ yr ...". We expect blue star to be in the minority in any galaxy, and so we see here. The point is that the stellar population of the galaxy is peculiar to that galaxy and its own specific star formation history (not all galaxies have the same distribution of gas from which stars form).

The "red" galaxy at 62 million light years is the giant elliptical galaxy NGC 1316, also known as the bright radio source Fornax A. But this galaxy is a merger remnant (Horellou, et al., 2001). The merger event(s) trigger short term bursts in star formation activity. What we see now is a galaxy that was very blue, due to active star formation, about 100,000,000 years ago, but star formation activity has dropped off since then. So you look at the "red" color, as far as GALEX is concerned, and think perhaps that the galaxy is far older than it really is (about 3 billion years since the major mergers that formed it; Kaneda, Onaka & Sakon, 2007). The appearance of this galaxy, as with NGC 300, is dominated by its own peculiar history, not by cosmic evolution.

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