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Fraser
2006-Oct-06, 07:02 PM
New images from NASA's Chandra X-Ray Observatory show the environment around the supermassive black hole at the heart of M87, a nearby giant elliptical galaxy. Chandra detected loops and rings in the hot gas that surrounds the galaxy. These loops are evidence of periodic eruptions near the supermassive black hole, which send shockwaves through the surrounding gas. These outbursts happen every few million years, and prevent the gas in the cluster from cooling to create stars.

Read the full blog entry (http://www.universetoday.com/2006/10/06/black-hole-stops-star-formation-in-elliptical-galaxy/)

pantzov
2006-Oct-07, 10:40 AM
this study, if confirmed by further observations in different areas, is of some significance because it might offer insight into the more distant future; a possibly much darker and depressing universe in which a greater number of super massive black holes arrest star formation over vast areas.

of course, this is just my imagination without facts :)

RussT
2006-Oct-07, 11:17 AM
this study, if confirmed by further observations in different areas, is of some significance because it might offer insight into the more distant future; a possibly much darker and depressing universe in which a greater number of super massive black holes arrest star formation over vast areas.

of course, this is just my imagination without facts :)

They are talking about Elliptical Galaxies here, which have pretty much completed their star making (they have used up most of their gas), sso what they may be seeing here is the 'shut off' mechanism.

The story is much different in younger galaxies.

http://www.newscientistspace.com/article/dn8025

antoniseb
2006-Oct-07, 01:32 PM
The story is much different in younger galaxies.

I agree with the general idea of what you are saying here, though I'd like to point out that the terms young and old with respect to galaxies may be misleading, since M31, which the NS article you've been dropping links to everywhere, formed very early in the history of the universe. What makes ellipticals "older" is only that for some reason, they've had their gas and dust mostly removed, and have stopped star formation, but they are basically the same age as each other.

RussT
2006-Oct-08, 10:43 PM
I'd like to point out that the terms young and old with respect to galaxies may be misleading, since M31, which the NS article you've been dropping links to everywhere, formed very early in the history of the universe.

[formed very early in the history of the universe]

Once again you are making the same assumption.

If, as I suspect, elliptical galaxies are the accumulation over time of the overall star formation in the disc of the entire galaxy + the result of all its dwarf galaxies 'falling' down the well to become part of said galaxy, which the accumulative effect is that the bulge and disc become less and less disc like, then the ellipticals are the oldest galaxies and have used up their gas, and not had it 'stripped'.

transreality
2006-Oct-08, 11:20 PM
Aren't ellipticals the result of their interaction history rather than age per se? The more collisions the faster there gas is used in star formation and/or stripped and/or distributed in an equilibrium. For statistical reasons most older galaxies will be have become elliptical. However, in theory, you could have isolated spirals that will virtually never relax to become a elliptical on their own. Maybe because it is the DM halo that is determining the shape.

However once interaction slows the rotation then gas can plunge towards the centre, expanding the blackhole and leading to the shock waves that are described in this article and which characterise the ellipticals behaviour appearance.

RussT
2006-Oct-08, 11:40 PM
Aren't ellipticals the result of their interaction history rather than age per se? The more collisions the faster there gas is used in star formation and/or stripped and/or distributed in an equilibrium.

Most current models have ellipticals being created by the merger of 'spiral' galaxies. If I remember correctly, antoniseb and I have both agreed we do not share this view. However, there is little doubt that ellipticals do have interaction with other galaxies, so I am just suggesting that most/all of that interaction is the 'pulling in' and accumulation of its dwarf galaxies (9-10).



However, in theory, you could have isolated spirals that will virtually never relax to become a elliptical on their own.

This could well be true. There are defintely size differences between spiral galaxies, so it could well be that only the largest (Most massive) spirals have the mass to be able to 'pull in' all their dwarfs.



However once interaction slows the rotation then gas can plunge towards the centre, expanding the blackhole and leading to the shock waves that are described in this article and which characterise the ellipticals behaviour appearance.

This sounds plausible, but the slowing itself could do this, and doesn't necessarily have anything to do with the 'expanding of the massive black hole'.

transreality
2006-Oct-09, 03:13 AM
I can't see how the infalling of the dwarfs which you possibly assume were satellites formed already in the main galaxies halo, could lead to the great change in morphology that a elliptical galaxy exhibits.

Is it not unreasonable that galaxies form in a rotating halo of dark matter? That it is the disruption of the rotation of this halo that leads to the transition from spiral to elliptical shape. And that the only way to effect the rotation of the halo is by large external influences; ie; the DM halos of other galaxies that pass nearby.

To link to the content of the article then it follows that as the galaxy slows down, gas will fall to the centre accreting to the black hole and making the explosions that then radiate outwards inhibiting further star formation by raising the gas temperatures.

RussT
2006-Oct-09, 07:26 AM
I can't see how the infalling of the dwarfs which you possibly assume were satellites formed already in the main galaxies halo, could lead to the great change in morphology that a elliptical galaxy exhibits.

I see, sorry if I wasn't clearer on this. No, I wasn't suggesting that dwarfs formed in the main galaxies halo. In fact each dwarf forms in its own, 'what they are calling a dark matter halo.

This site shows that dwarfs are basically in a 10/1 ratio with the galaxies, and once on the site you can see where our dwarfs are in relation to the Milky Way.
http://www.atlasoftheuniverse.com/sattelit.html



great change in morphology that a elliptical galaxy exhibits.

I am still trying to find a paper I saw on 'edge on' BCD's that showed that the disc width (edge on) was very much thinner than regular galaxies. There is also quite a difference in different 'bulge' sizes and apparent widths along with different apparent 'core' sizes. So, when you add all that up, the longer that a galaxy has to make its own stars and then the additional dwarf galaxies stars and then the dwarf promotes even more star formation, then the bulge is spherical and the disc is no longer a flat structure, as all of this adds to the slowing of the galaxies rotation.




Yes, it it reasonable, and I believe it does, but the deeper question is, what makes this Dark Matter of space, 'out in the middle of nowhere' rotate in a spiral? When they calculate the mass of the SMBH though, it is not nearly massive enough to rotate the whole galaxy at the speed they see it at.
So what do they conclude...that the SMBH can't be the mechanism for the whole galaxies rotation. But this is not the whole story.

[QUOTE=transreality]
And that the only way to effect the rotation of the halo is by large external influences; ie; the DM halos of other galaxies that pass nearby

From what I have seen, it appears that there is less and less DM needed to explain the rotation curves in direct relation to the abundance of stars in any galaxy. In other words, BCD's and LSB's need alot of DM, regular galaxies need quite a bit, and ellipticals need the least. So its not more DM being added.

From the article;
[These outbursts happen every few million years, and prevent the gas in the cluster from cooling to create stars] my bold.

I see, this is talking about gas outside the galaxy being heated, so it can't cool to make stars.

antoniseb
2006-Oct-09, 11:46 AM
It is likely that there are numerous mechanisms for creating small ellipticals from gas and dust bearing galaxies (spirals & irregulars). There is one famous example of a galaxy falling in toward the center of a giant cluster, and we can see that it is in the process of having its gas and dust stripped out of it right now.

This can't be the only mechanism, since it requires a massive cluster, but it shows one way that this happens. The Bullet cluster may be showing us another way. Two similar sized spirals pass through each other. The stars keep going, while the gas and dust stay behind and form a third (dark-matter poor) galaxy.

transreality, you are pretty new here. Please note that RussT is exploring observations that may support ideas related to the Steady State Universe. Some of his analysis reflects this interest. Likewise, I have a point of view, that while closer to mainstream does not embrace all mainstream ideas about galaxy formation. We are both looking for facts and undertanding here. Your view might differ from ours. We'll argue our cases, but won't be insulted by you disagreeing.

transreality
2006-Oct-09, 11:07 PM
Thank-you Antoniseb, I am grappling with these ideas too; essentially if it is necessary to accept the existance of dark matter, then what is the structure of the dark matter universe? I think that the galaxies could be forming inside very large clouds of dark matter that are rotating perhaps due to turbulence imparted in the big bang, and that differences in the interactivity of dark and baryonic matter are resulting in the visible structure. However, I see that this view includes assumptions that not everyone may share.



From what I have seen, it appears that there is less and less DM needed to explain the rotation curves in direct relation to the abundance of stars in any galaxy. In other words, BCD's and LSB's need alot of DM, regular galaxies need quite a bit, and ellipticals need the least. So its not more DM being added.

Or the more interaction a galaxy experiences the closer the galaxy appears to be controlled by gravity as we understand and less by its DM halo. Perhaps the halo is stripped from an elliptical galaxy.



From the article;
[These outbursts happen every few million years, and prevent the gas in the cluster from cooling to create stars] my bold.

I see, this is talking about gas outside the galaxy being heated, so it can't cool to make stars.

Can this observation test our theories? If star formation is the main process leading to evolution of ellipticals then in a cluster that is inhibiting star formation old exhausted spirals will proliferate, if interaction between galaxies is the main process leading to ellipticals then smaller ellipticals will proliferate since star formation will cease growing spirals.

RussT
2006-Oct-10, 08:43 AM
It is likely that there are numerous mechanisms for creating small ellipticals from gas and dust bearing galaxies (spirals & irregulars). There is one famous example of a galaxy falling in toward the center of a giant cluster, and we can see that it is in the process of having its gas and dust stripped out of it right now.


This can't be the only mechanism, since it requires a massive cluster, but it shows one way that this happens. The Bullet cluster may be showing us another way. Two similar sized spirals pass through each other. The stars keep going, while the gas and dust stay behind and form a third (dark-matter poor) galaxy.

I thought we were talking about galaxy formation, not collisions.

[while the gas and dust stay behind and form a third (dark-matter poor)galaxy]

I thought this article was saying that the stars and gas stayed and the Dark Matter kept going. And I have never seen anything saying a third galaxy is formed out of a two galaxy collision, and 'if' one was, why would you think it would be 'dark matter poor'?



Please note that RussT is exploring observations that may support ideas related to the Steady State Universe.

Whoa, careful...I am promoting the correctness of General Relativity even more strongly than mainstream...Do you think that 'could' work under part of the Steady State universe?

RussT
2006-Oct-10, 09:36 AM
Or the more interaction a galaxy experiences the closer the galaxy appears to be controlled by gravity as we understand and less by its DM halo. Perhaps the halo is stripped from an elliptical galaxy.

The Dark Matter halo is a bit confusing. Non-Baryonic DM permeates the entire galaxy and extends to the outer edges and beyond to make the galaxy rotation curves come out right. So it is the beyond, all around the galaxy they are calling the halo.

My view is simply that DM is all of space, so there are no halos. The only reason so far that we even know that there must be DM is the galaxy rotation curves (without alot of extra non-baryonic DM, the stars would be flying out of the galaxies), and the cluster gravitational dynamics. So the only way we can see or detect the DM is when it is in proxomity to baryonic matter, so the rest of space is DM too, we just can't see it.

I am not sure if they think that there are any of these 'dark matter halo's' floating around out there with 0 baryonic matter in them, some baryonic matter in them, or all their baryonic matter in them, just waiting and waiting for 'whatever' conditions to be right to begin their star making process. Maybe antoniseb can clue us in on that from his perspective.



Can this observation test our theories? If star formation is the main process leading to evolution of ellipticals then in a cluster that is inhibiting star formation old exhausted spirals will proliferate, if interaction between galaxies is the main process leading to ellipticals then smaller ellipticals will proliferate since star formation will cease growing spirals.

Sorry, this doesn't sound viable. Stars are really only made in the galaxies they are in, not out in the IGM where all the cluster gas they are talking about is, which as they said, is too hot to be star forming regions anyway.

antoniseb
2006-Oct-10, 10:48 AM
I thought we were talking about galaxy formation, not collisions.

while the gas and dust stay behind and form a third (dark-matter poor) galaxy
I thought this article was saying that the stars and gas stayed and the Dark Matter kept going. And I have never seen anything saying a third galaxy is formed out of a two galaxy collision, and 'if' one was, why would you think it would be 'dark matter poor'?

If you have two galaxies (or clusters of galaxies) heading toward each other, each with the normal mix of dark matter and reactive matter, when they collide, the dark matter will be affected gravitationally, but not by friction, so each particle will accelerate on the way in, and slow down on the way out, and some randomness will be introduced from the gravitational interactions with stars and other small bodies along the way. Likewise stars and planets will do the same thing. What could stop them? But the Gas and dust collide and are separated from the two sets of stars and dark matter. So the two galaxies pass through each other with their dark matter and old star population, but with very reduced gas and dust. Meanwhile, the gas and dust collect into a cloud with roughly the average velocity of the two galaxies combined. This cloud of gas and dust has less than the usual amount of dark matter. The two original galaxies are now dark matter rich, and will soon have only old stars.

antoniseb
2006-Oct-10, 12:01 PM
Here (http://arxiv.org/abs/astro-ph/0610216) is an interesting short paper about the red-shift cutoff for Radio-loud QSOs. The paper sys that there are very few of these things prior to z=3, and does a good job of ruling out radio-opaque media as an explanation.

The author equates the radio-loud period of QSOs to their formation (which I'm not sure I agree with). I bring this paper up becuase if it is true, then the model I've been using will need some modification. It's an interesting observation.

RussT
2006-Oct-10, 11:22 PM
when they collide, the dark matter will be affected gravitationally, but not by friction,

If not by friction, then by what?

If DM does not interact with baryonic matter, then it should also be true that baryonic matter cannot affect DM (accept of course by causing a 'dent' (gravity well) in it, where ever that baryonic body is at any given point in time in its trajectory, but it can't carry or pull DM with it).



so each particle will accelerate on the way in, and slow down on the way out, and some randomness will be introduced from the gravitational interactions with stars and other small bodies along the way.

So, you do know the speed at which DM travels? to be able to say that it speeds up or slows down?

Besides putting a 'dent' (gravity well) in the fabric of space/time, there is only one thing that can actually AFFECT DM 'space', and that is the formation of a Massive Black Hole. If you would like to go into more detail about this, I will be happy to.



So the two galaxies pass through each other with their dark matter and old star population, but with very reduced gas and dust. Meanwhile, the gas and dust collect into a cloud with roughly the average velocity of the two galaxies combined. This cloud of gas and dust has less than the usual amount of dark matter. The two original galaxies are now dark matter rich, and will soon have only old stars.

This sounds as though you are trying to treat the DM like it is baryonic matter, but seperate. All baryonic matter interacts with itself, DM on the other hand, does not interact with baryonic matter or itself.

transreality
2006-Oct-10, 11:56 PM
If the baryonic matter is gravity bound to the core of the galaxy, and the core of either galaxy is deflected by the interaction, then the baryonic component could seperate from the dark matter component.

This could be a scenario cause a spiral to relax into an elliptical.

antoniseb
2006-Oct-11, 12:23 AM
This sounds as though you are trying to treat the DM like it is baryonic matter, but seperate. All baryonic matter interacts with itself, DM on the other hand, does not interact with baryonic matter or itself.

I'm not sure I follow you here. I am describing the behavior of dark matter on the mainstream view that it is composed of Weakly Interacting Massive Particles. So we do know the range of velocities that these particles must have to compose the mass of the galaxy, and because the dark matter makes up five or six times as much mass as the protons and neutrons in the galaxy, DM's momentum is not affected much by the gravity of the luminous matter.

I am just looking at the dynamics of such a system. I'm not asserting any ideas about black holes or the fabric of space, except that WIMPs have mass.

RussT
2006-Oct-11, 02:02 AM
This cloud of gas and dust has less than the usual amount of dark matter. The two original galaxies are now dark matter rich, and will soon have only old stars.

When you come to this conclusion, you are saying that there are different densities for DM in different vicinities, and I am saying that the density of DM is always the same everywhere.

So actually your example above should be the opposite, because you yourself have said that WIMPS are inside baryonic mass bodies, and I agree, and I am saying that they (WIMPS) are travelling at "C" through them.

So, that means that in the First Dark Matter Galaxy Found (HI only) that huge amounts of DM are needed to explain their rotation curves, BCD's and LSB's need a little less DM (because their stars contain some of the DM), HSB's need even less DM (because more stars are containing more DM), and finally, ellipticals need the least DM because of so many stars containing DM.

So, it is just an illusion, if you will, because all of the DM is there, it is just that as more stars and stuff are made, they are 'borrowing' more and more of the DM.

BigDon
2006-Oct-11, 02:06 AM
Not to change the topic but does anyone have a guess as to the scale of the photo provided? And the distance to said object?

antoniseb
2006-Oct-11, 11:58 AM
I am saying that the density of DM is always the same everywhere.
I am saying that they (WIMPS) are travelling at "C" through them.

The dark matter you describe above does not explain the phenomena we are seeing, such as lensing by galactic clusters and galaxy halos. It is definitely not the mainstream view of CDM. HDM is only a small fraction of the mass of the universe.

John Mendenhall
2006-Oct-11, 05:49 PM
Show me the dark matter!

Remember, dark matter is invoked because we have no better explanation for spiral galaxy rotation curves and galaxies being bound in clusters when in both cases Newtonian mechanics indicates dispersion at the measured velocities. I think it is unwise at this point to make big assumptions about the influence of DM on the evolution of the universe. Yes, it could be, but I would like a little better evidence than "Well, if it isn't dark matter, then what is it?"

I'm going to beat this to death. I promise not to post anything about dark matter for a month.

I break my promise already. Can we call my views 'anti-dark-matter'?

antoniseb
2006-Oct-11, 06:05 PM
dark matter is invoked because we have no better explanation for spiral galaxy rotation curves and galaxies being bound in clusters when in both cases Newtonian mechanics indicates dispersion at the measured velocities.
Can we call my views 'anti-dark-matter'?

Weak lensing studies have allowed us to make maps of the dark matter densities in large clusters and elsewhere. I think those studies show you the dark matter.

If you choose not to believe those studies, then presumably at some point in the near future we will start to detect events with the individual particles. Experiments to this end are getting scaled up now.

Can we call your views anti-dark-matter? If you like. I don't get te impression that you'd oppose its existence if it were observed more directly, but rather you are of the opinion that astronomers are accepting it as observed to the degree that they are blinding themselves to other alternatives.

This kind of discussion really belongs in the ATM section.

RussT
2006-Oct-12, 08:53 AM
The dark matter you describe above does not explain the phenomena we are seeing, such as lensing by galactic clusters and galaxy halos. It is definitely not the mainstream view of CDM. HDM is only a small fraction of the mass of the universe.

It is the 'gravity well' of the baryonic matter of the whole galaxy or the cluster that is causing the lensing...the ponderable matter causing a distortion of space/time (a 0 energy background of inert DM traveling at "C").

Are you saying that the mainstream view is that there are *2* particles that are traveling through baryonic matter?

antoniseb
2006-Oct-12, 10:47 AM
1. It is the 'gravity well' of the baryonic matter of the whole galaxy or the cluster that is causing the lensing...the ponderable matter causing a distortion of space/time (a 0 energy background of inert DM traveling at "C").
2. Are you saying that the mainstream view is that there are *2* particles that are traveling through baryonic matter?

1. How can what you are describing produce the effects we are seeing? It can't unless there is twenty something times as much ponderable matter as we can see in those clusters, AND that ponderable matter must not be interacting with itself AND a substantial amount of that ponderable matter must be invisibly flying around outside but near the central giant elliptical AND that ponderable matter must not be causing the stars in the giant elliptical to orbit extremely fast. This just isn't ponderable.

2. I don't know what you mean. Perhaps you mean that I am talking about neutrinos as Hot Dark Matter and some heavy particle (perhaps Neutralinos or some other sParticle) as Cold Dark Matter. If that is what you mean by 2 then yes.

GOURDHEAD
2006-Oct-12, 01:05 PM
Have limits been established for the interaction weakness of WIMPs? Is the interaction exclusively gravitational?

antoniseb
2006-Oct-12, 01:27 PM
Have limits been established for the interaction weakness of WIMPs? Is the interaction exclusively gravitational?
Upper limits yes, lower limits no. These limits are specific to different kinds of possible WIMPs. It is possible that some type of WIMP that has never yet been considered, and has very different properties than we expect is the culprit.

RussT
2006-Oct-13, 10:39 AM
1. How can what you are describing produce the effects we are seeing? It can't unless there is twenty something times as much ponderable matter as we can see in those clusters, AND that ponderable matter must not be interacting with itself AND a substantial amount of that ponderable matter must be invisibly flying around outside but near the central giant elliptical AND that ponderable matter must not be causing the stars in the giant elliptical to orbit extremely fast. This just isn't ponderable.

I am not saying the ponerable matter is causing this kind of lensing. I know galaxies can be lenses, but it is really the DM that is doing the lensing, and that is because ponderable matter distorts space/time.

If you still think this is wrong, just say why.



2. I don't know what you mean. Perhaps you mean that I am talking about neutrinos as Hot Dark Matter and some heavy particle (perhaps Neutralinos or some other sParticle) as Cold Dark Matter. If that is what you mean by 2 then yes.

I explained my thoughts on this somewhere, but maybe not to you.

First of all, I have very specific reasons for what I am saying about DM, I'm not just guessing.

When you are considering neutrinos, you know they are traveling at relativistic speeds, so you consider them as HOT non-baryonic matter...hot DM. Maybe they have a tiny Planck mass and maybe they don't, as far as you know.

But here trinitree says;
Quote:
Originally Posted by trinitree88
RussT. Don't wash out the neutrino sea, here. Astromark is incorrect in saying that space is nothing, and empty. If the proponents of massive neutrinos turn out to be correct, then they must be subluminal or we are mandated to trash The Special Theory of Relativity. Saving the STR would give a limiting velocity to those neutrinos making up the "sea" (earlier work,not by grav).]

So, they should be traveling at "C".

Now, because of the way you are 'seeing' CDM, as non-baryonic DM in the galaxy rotation curves, just as extra gravity, you don't know its speed and since it is away from baryonic matter (not coming from the sun and going through the earth), you see it as 'cold' and therefore 'slow'.

So, all I am saying is...that if it is WIMPS, that it is non-baryonic Planck mass particles, and since it is 'going through' baryonic matter, that it HAS to be traveling at 'C', otherwise it would have to 'react' to the baryonic matter all the time.

So the only real difference between the hot and the cold wimps, is where we are seeing them, and they are one and the same.

antoniseb
2006-Oct-13, 11:51 AM
that if it is WIMPS, that it is non-baryonic Planck mass particles, and since it is 'going through' baryonic matter, that it HAS to be traveling at 'C', otherwise it would have to 'react' to the baryonic matter all the time.

Can you go into more about how you make this connection? I don't see why travelling at less than 'C' makes non-reactive particles have to react or interact.


I know galaxies can be lenses, but it is really the DM that is doing the lensing, and that is because ponderable matter distorts space/time.

Are you saying that the ponderable matter distorts space-time six to twenty times as much as its gravity would otherwise distort space-time? Up till now, I thought you were only talking about gravity. If this is the case why are some galaxies richer in this distortion capability than others?


But here trinitree says;

Trinitree is a smart guy, but his dive into ATM is with respect to neutrinos. You can't take his statements about neutrinos as entirely reflecting accepted science. He argues that neutrinos can't have mass.

Hamilcar
2006-Oct-18, 05:39 PM
Most current models have ellipticals being created by the merger of 'spiral' galaxies.

The models are wrong here. Massive early-type galaxies like M87 are hugely alpha-enhanced, so their stellar populations can't have been formed in a disk where star-formation went on for extended periods of time. If they are disk-disk merger products, then they must have formed in the very, very early universe. With a velocity dispersion as high as that of M87, [alpha/Fe] points to a star-formation timescale of only a few hundred Myr.

Semi-analytic models have their problems and creating alpha-enhanced massive galaxies at high redshift is one of them. We will see how proper prescriptions for AGN feedback will fix this.

RussT
2006-Oct-22, 09:03 AM
Can you go into more about how you make this connection? I don't see why travelling at less than 'C' makes non-reactive particles have to react or interact.

It would seem that the slower the particle, even a very tiny Planck size DM particle, the more its rest mass could come into play.



Are you saying that the ponderable matter distorts space-time six to twenty times as much as its gravity would otherwise distort space-time?

I still don't see why you think that this is what my interpretation means.



I thought you were only talking about gravity. If this is the case why are some galaxies richer in this distortion capability than others?

I would asume that much larger galaxies have richer sidtortion than smaller ones, and it could also have to do with angles of inclination for the lens.



Trinitree is a smart guy, but his dive into ATM is with respect to neutrinos. You can't take his statements about neutrinos as entirely reflecting accepted science. He argues that neutrinos can't have mass.

Well, I don't know how smart he is (he he he), but it would seem that he is pretty knowledgable. More than that though, he was actually doing 'good' science here, because he showed what it could mean if they had mass and if they didn't (which should always be done for any phenomena, show what it could mean both ways until we are sure we have a workable model!).

In chose the massive example in my statement. He may prefer the massless case in his models of how things work in any particular realm.

BUT, it should always be shown both ways!

RussT
2006-Oct-22, 09:17 AM
The models are wrong here. Massive early-type galaxies like M87 are hugely alpha-enhanced, so their stellar populations can't have been formed in a disk where star-formation went on for extended periods of time. If they are disk-disk merger products, then they must have formed in the very, very early universe. With a velocity dispersion as high as that of M87, [alpha/Fe] points to a star-formation timescale of only a few hundred Myr.

Semi-analytic models have their problems and creating alpha-enhanced massive galaxies at high redshift is one of them. We will see how proper prescriptions for AGN feedback will fix this.

[With a velocity dispersion as high as that of M87, [alpha/Fe] points to a star-formation timescale of only a few hundred Myr.]

This is very interesting. Are you talking about the whole galaxy?

[are hugely alpha-enhanced]

I looked this up, but do you know more about this that you could share?

[With a velocity dispersion as high as that of M87]

Does this mean there should be more DM or less DM?

Do you think there is any possibility that M87 is a face on galaxy, where its core is responsible for most of the luminosity, and that, over some time, this could happen?
http://www.spacedaily.com/news/stellar-chemistry-05x.html

transreality
2006-Oct-23, 04:25 AM
A picture of M87 that shows the globular clusters shows no signs of organisation of the halo into spiral arms.

http://antwrp.gsfc.nasa.gov/apod/ap040616.html

Okay, so what is possible is that even without any external interaction a large elliptical might form in isolation because if it is large enough an active galactic nucleus will form, star formation will become retarded by the increase in the temperature of the gas, so that the galaxy will never take on a spiral appearance.

The Bad Astronomer
2006-Oct-23, 04:41 AM
There is also the issue that M87 sits in the gravitational center of a relatively massive cluster and is certainly the product of many galactic collisions. Last I read, its mass was a trillion solar masses, and galaxies probably don't get that big without a lot of mergers. Now that I think about it, it only has one core, so it hasn't had a collision in a while. Some galaxies (like Andromeda) have multiple cores, indicating they recently ate another galaxy.

Hamilcar
2006-Oct-23, 10:13 AM
[With a velocity dispersion as high as that of M87, [alpha/Fe] points to a star-formation timescale of only a few hundred Myr.]

This is very interesting. Are you talking about the whole galaxy?

a/Fe doesn't show any strong gradients; neither does metallicity or age. There *are* gradients, just not significant ones.


[are hugely alpha-enhanced]

I looked this up, but do you know more about this that you could share?

alpha/Fe is the ratio of alpha-process elements to iron. It's been called the cosmic clock because it's a measure of the timescale on which star-formation occurred.

Very simplistically: alpha-elements are produced by Type II supernovae, which essentialyl trace ongoing star-formation, while iron is produced in Type Ia supernoave, which have a significant time delay.



[With a velocity dispersion as high as that of M87]

Does this mean there should be more DM or less DM?


I am not sure what DM has to do with this. The Mass-to-Light ratios of the centers of early-type galaxies imply there can't be much DM there.


Do you think there is any possibility that M87 is a face on galaxy, where its core is responsible for most of the luminosity, and that, over some time, this could happen?
http://www.spacedaily.com/news/stellar-chemistry-05x.html[/quote]

I don't think so. M87, like most Virgo galaxies, has excellent multiwavelength coverage from X-ray to radio. If M87 had spiral arms, we'd have seen them long ago. In fact, I have the GALEX mosaic of Virgo on my hard drive. M87 shows no spiral arms. : )

Hamilcar
2006-Oct-23, 10:15 AM
There is also the issue that M87 sits in the gravitational center of a relatively massive cluster and is certainly the product of many galactic collisions. Last I read, its mass was a trillion solar masses, and galaxies probably don't get that big without a lot of mergers. Now that I think about it, it only has one core, so it hasn't had a collision in a while. Some galaxies (like Andromeda) have multiple cores, indicating they recently ate another galaxy.

The problem with the 'merger' scenario is that too many (dry) mergers dilute the known element abundance relations with mass and so hugely massive galaxies like M87 probably can't have built the bulk of their stellar mass from mergers.

Making massive early-type galaxies in the LambdaCDM universe is tricky.

RussT
2006-Oct-23, 10:54 AM
"This nearby galaxy represents one of our possible histories, in which stars developed first in the galaxy core and then later in the arms."

http://www.spacedaily.com/news/stell...istry-05x.html

This quote out of the article looks to be more and more likely, and I would very much like to know if you think that the articles assessment, that the core stars 'must' be 10 Gyrs old is possibly invalid. That certainly leaves a huge discrepancy between when the core started star formation to when the arms did!

Here is my favorite for core formation first!!!

http://www.narrabri.atnf.csiro.au/public/images/ngc2915/



I am not sure what DM has to do with this. The Mass-to-Light ratios of the centers of early-type galaxies imply there can't be much DM there.

Are you saying the M87 appears to be a huge young galaxy core only?

Hamilcar
2006-Oct-23, 11:08 AM
"This nearby galaxy represents one of our possible histories, in which stars developed first in the galaxy core and then later in the arms."

http://www.spacedaily.com/news/stell...istry-05x.html

This quote out of the article looks to be more and more likely, and I would very much like to know if you think that the articles assessment, that the core stars 'must' be 10 Gyrs old is possibly invalid. That certainly leaves a huge discrepancy between when the core started star formation to when the arms did!

I can't access that link. : (
The stellar populations of massive early-type galaxies are pretty clear in their element abundances: they formed a long time ago and on a short time scale. There's just no way around that. The stars in a huge galaxy like M87 can't possibly have formed in a disk, unless that disk was almost immediately destroyed in the early universe. Star-formation in disks is extended and continues for a long time; the a/Fe rations of massive galaxies preclude such a star-formation history. M87 did NOT form from a massive disk-disk merger below z ~ 1.



Here is my favorite for core formation first!!!

http://www.narrabri.atnf.csiro.au/public/images/ngc2915/

BCDs aren't analogues of massive arly-types.


Are you saying the M87 appears to be a huge young galaxy core only?

Huh? No, not at all. M87 is very old. I thought DM referred to Dark Matter?

RussT
2006-Oct-24, 09:18 AM
http://www.spacedaily.com/news/stellar-chemistry-05x.html
Here is the link again.

And my question again;
[This quote out of the article looks to be more and more likely, and I would very much like to know if you think that the articles assessment, that the core stars 'must' be 10 Gyrs old is possibly invalid. That certainly leaves a huge discrepancy between when the core started star formation to when the arms did!]



I can't access that link. : (
The stellar populations of massive early-type galaxies are pretty clear in their element abundances: they formed a long time ago and on a short time scale. There's just no way around that.

[they formed a long time ago and on a short time scale. There's just no way around that]

There is a way...they formed on the sqme time scale as all of the galaxie in the universe do...one day at a time.



M87 did NOT form from a massive disk-disk merger below z ~ 1.

This is good to know.



Huh? No, not at all. M87 is very old. I thought DM referred to Dark Matter?

Sorry, this was a misread/misunderstanding on my part from something you had said earlier. I took this to mean 'recently'... [With a velocity dispersion as high as that of M87, [alpha/Fe] points to a star-formation timescale of only a few hundred Myr.]

Hamilcar
2006-Oct-24, 09:45 AM
http://www.spacedaily.com/news/stell...istry-05x.html
Here is the link again.

And my question again;
[This quote out of the article looks to be more and more likely, and I would very much like to know if you think that the articles assessment, that the core stars 'must' be 10 Gyrs old is possibly invalid. That certainly leaves a huge discrepancy between when the core started star formation to when the arms did!]

The two cases don't compare, it's a question of mass. NGC 4625 isn't a terribly big galaxy, I could not find a velocity dispersion, but its M_K isn't too big. Small early-type galaxies are know to have low alpha-enhancements and so can have some of their stars form in faint disks or spiral arms.

The same is impossible for the stars in a galaxy as big as M87. a/Fe is so high that virtually none of its stars can have formed in a disk where star-formation lasts for extended periods of time. The stellar population of M87 to the best of my knowledge is pretty uniform in age, metallicity and a/Fe.


[they formed a long time ago and on a short time scale. There's just no way around that]

There is a way...they formed on the sqme time scale as all of the galaxie in the universe do...one day at a time.

The data say: no. Massive early-types formed on short time scales.