Quasars and Cosmology

turbo

Any model must not only explain observations, but admit to falsification by those observations.

The puzzles (anomalous observations) cannot be solved in a vacuum, one at a time. There are many adjustable parameters in cosmology that can be tweaked to "allow" the fitting of one observation or another (at least to the satisfaction of a BB adherent), even if the proposed fix is implausible and/or unsupported by any evidence.

I'm already involved in another paper with Ari and Dave (and another co-conspirator) and expect to have it published in the same journal as the last one. I don't have time to become a cosmologist right now, nor the inclination to try to get published as one, as long as the field is dominated by BB/LCDM

LCDM seems to be able to accommodate many things (retro-dictions, not predictions) in part because there are so many parameters that can be tweaked.

If Fotini Markopoulou is right, and we see frequency-dependent delays in the arrival times of Gamma rays (more energetic=slower) then we will have a reason to consider space a transmissive medium with variable optical characteristics. That would shake things up and might help make cosmology a more exact science. Waiting for that.

matt.o

The point you seem to miss, turbo-1, is that this problem is more likely to be one for galaxy evolution models at high redshift, not one for LCDM.

And to turn this question around, if JWST does not find what you propose, will you buy me a case of Australia's finest beer?

oldman

Nereid, your strength seems to be cross-examination, judging from numerous posts in this most illuminating thread. Since cosmology is a subject that in the absence of experimentation depends on ratiocination and analysis of circumstantial evidence, your stance as council for the defence of the current consensus is entirely appropriate. I, for one, certainly enjoy it.

I see that you are billed as 'retired staff', which could mean that you have both the time and perhaps the inclination to broaden your perspective. If so, I recommend reading a somewhat romantic detective novel that I believe should be part of any cosmologist's education. This is "Trent's Last Case", by E.C. Bentley. It's the classic of its genre and would provide a good start to 2009.

George Jones

This has been re-opnened and split.

Discussion of the astrophysics of quasars along the lines that Jonathan Scott introduced should take place in the Astrophysics thread

http://www.physicsforums.com/showthread.php?t=282478.

Discussion about the mathematics (differential geometry) of an (almost) isolated Schwarzschild solution should take place in the thread

http://www.physicsforums.com/showthread.php?t=272909,

which will re-opened later tonight or tomorrow morning.

turbo

Well, I don't make bets, but I am relying on logical expectations, here. The highest-redshift SDSS quasars are all single-band detections (no further filters to play the comparative-image game) and they are right at the limits of detectability (faint) with their 'scope. z~6.5 is not some magic number at which the highest-redshift quasars reside. It is the limit of detection of the SDSS equipment.

Absent some good theoretical reason to believe that these are the most distant quasars, it is reasonable to believe that quasars at higher and higher redshifts will be discovered once we have an instrument that is outside the atmosphere, and with deeper IR capabilities. Indeed, this is predicted by the authors of the paper that Nereid linked. http://arxiv.org/abs/0812.3950

Nereid

I missed some key points in my earlier reply to this post ... There are four things in this list, and many not in it (more later). I think it's worth taking a closer look at the list, as presented, because I think its brevity hides some misunderstandings (or worse).

Have you seen any papers in peer-reviewed journals that explain how the z~6.5 quasars can be so highly metallized - turbo-1

Presumably "the z~6.5 quasars" refers to the 19/20 quasars mentioned in Strauss' video, which have 5.74 < z < 6.42. Of course, a quick search through the literature turns up plenty of papers which provide good answers to the general question of how the nuclear regions of high-z (>5.7) AGNs can attain the observed metallicities.

For example: In Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey (non-SDSS detected high-z quasars) we read (p8):At ~1000M⊙yr-1 it takes only ~a million years to produce ~a billion sols of stars. Add to that the increasingly strong observational results consistent with the IMF of nuclear starbursts being (very) top heavy (i.e. proportionately many more ~>10 sol stars than in the IMF of the placid star forming regions), and work on "Dark Stars", and ...

For sure, lots more work to do, but it would seem this question can be answered in the affirmative.

and show no evolution with redshift - turbo-1

The brevity of this statement makes its literal reading ridiculous ... of the 19/20 z>5.7 quasars mentioned in the Strauss video, no comments about "evolution with redshift" were made. Presumably turbo-1 meant that AGNs show no evolution with redshift, over the range ~0.1 < z ~6.5. If so, to ask a single paper to explain this reported result AND the observed metallicity of ~20 z>5.7 quasars is a bit extreme (unless it were a review paper).

I'll skip the next point ("no lensing"), if only because I can't track down where Strauss mentions this in the video (and turbo-1 has yet to provide anything else for any reader to try to figure out what he's referring to).

and a soaring LF at z>3 - turbo-1

As with the "no evolution with redshift", brevity makes for ambiguity.

For starters, the second graph on slide 63 does not have any datapoints for z>5; for seconds the datapoint at z=4.75 has an enormous error bar; for thirds at the time (2005) the only z>5.7 quasars observed were highly luminous, making it impossible to estimate an LF (in this redshift range).

And, as I have already written (in an earlier post in this thread), there are indeed "papers in peer-reviewed journals that explain" how the "LF slope increases at z=3 and above" (to quote from that Strauss slide).

As above, if turbo-1 is looking for a single paper (other than a review paper) which covers all four of his points (suitably restated to remove ambiguities and misunderstandings), then it's no wonder he hasn't seen any!

Now for the things NOT in the list, taken, you will recall, from the Strauss video.

The first slide, in the Supporting Material, has four bullet points (I'm quoting):

• The nature of quasars at the highest redshifts.
• Using quasars to probe the epoch of reionization.
• The luminosity function of quasars, from low redshift to high.
• Type II quasars and the effects of reddening on quasars.

turbo-1's points presumably come under the first and third; what of the other two?

The second ("Using quasars to probe the epoch of reionization") is surely pertinent to LCDM cosmological models (or whatever other label turbo-1 has used) - it is a direct prediction of 'the BBT' (for example, the Gunn-Peterson trough, predicted in 1965!). The story not told (by turbo-1) is that the SDSS-based observations have nicely confirmed the general features and shed some light on details that could not be tested until then (2005). Interestingly, they also shed some light on the rate of star formation in the earlier (z >~6.5) universe, the role of (AGN) accretion and (galaxy) mergers ... which in turn are, of course, pertinent to how high-z quasars came to have their observed metalicities.

IOW, a nice example of modern science in action, doing what it does best.

The fourth ("Type II quasars and the effects of reddening on quasars") is part of the solving of a (now) rather old puzzle - how well does the unified model of AGNs actually account for the observations? This is not a cosmological puzzle (except, perhaps, for turbo-1, or only in the most general sense), but it's pertinent to some of the points raised, by both turbo-1 and JS.

The good news is that several predictions, from the unified AGN model, have been nicely validated by the observations Strauss briefly mentions. One possible implication of this work is to get a better handle on AGNs, and so help in the elucidation of the evolution of the LF.

The bad news is for JS ... this work is yet further confirmation that the mainstream understanding of quasars (AGNs) is right, and that they have "intrinsic redshifts" equal to zero (within the observational error bars).

turbo

Just so we don't end up with choppy, messy posts, I'll try to take on the ideas one at a time. First off, as Strauss mentioned Mg II and Fe II are created in different types of supernovae, so it was expected that there would be some evolution in the concentrations of these metals with redshift, both in absolute and relative concentrations. No such evolution was found, and the the redshift-corrected spectra of low-redshift and high-redshift quasars are essentially the same. We know (or believe) from our models of synthesis of elements in stars that Fe is the heaviest element that can be produced by fusion, and it is a slow process. The iron is predominantly distributed by type Ia SN. This requires white dwarf stars, relic cores of intermediate-mass stars that have left the main sequence and gone red-giant, then planetary nebula. This process takes billions of years. Where did all the Fe at redshift 6.5 come from?

turbo

Then there is the matter of how BHs of several billions of solar masses could have formed by z~6.5. From the paper Nereid linked earlier. Bold added - formation of quasars and the SMBHs that power them is a cosmological problem.

http://arxiv.org/abs/0812.3950Some of the difficulties are mentioned here, including the fact that the BHs would have to have grown faster than allowed by the Edding accretion rate AND this supposes that such rapid accretion is not slowed by radiative feedback. One might expect that such rapid accretion would be very energetic, so ignoring the radiative feedback that should slow the accretion rate is probably not a good idea.

Then we have speculation about stars being powered by dark matter annihilation rather than fusion. DM is the cosmologists' dream. It cannot be detected like baryons - it is supposed to interact only weakly with baryons and itself, and then only gravitationally, yet we are to consider that DM annihilation is energetic enough to power stars? DM flattens rotation curves of spirals, provides extra gravitational bonding to clusters, and now this elusive stuff is reactive enough to have powered stars in the early universe through annihilation. Whew!

Clearly, the authors expect to discover quasars at higher and higher redshifts, yet their proposed mechanisms for the formation of quasars even at z~6 are problematic and implausible, even with generous allowances, such as ignoring radiative feedback during super-Eddington accretion. With such difficulties accommodating z~6 quasars, how will they shoehorn z~10 quasars into the ever-shrinking mass and time budgets looking back to higher redshifts?

turbo

No lensing. Strauss explains that with the very high column densities to the most distant quasars, it was expected that some intervening masses would have lensed at least a fraction of them, brightening them and distorting them away from point-like appearances. None of the z>5.7 quasars in the SDSS sample are lensed. The sample from z=5.7-~6.5 is small, so this might be explained by coincidence alone. I don't know what assumptions the SDSS team made when calculating the probability that these quasars would be lensed. I may have to dig around their earlier papers to see if they published that.

turbo

The luminosity function curve slope changes fairly abruptly after redshift z~3, with no theoretical explanation why this should be. Strauss spends some time on this puzzle around 50 minutes into the presentation. With no redshift-dependent evolution in any metric by which SDSS examined these quasars, why should the slope of the LF curve show such a strong dependence on redshift?

granpa

what does 'The luminosity function curve slope changes fairly abruptly after redshift z~3' mean?

turbo

Please watch the video of Strauss' presentation and his PowerPoint slides as he explains. It's a 1-hour presentation, but well work the investment in time, since it summarizes findings that had been published in years of SDSS papers. The link is in the OP of this thread.

Here is the most recent SDSS paper on LF that I could find with a brief search. Essentially, the data suggests some type of cosmic downsizing for quasars in which the most massive quasars were most actively accreting at high redshifts. If you watch the presentation to see the plots, you'll see a distinct "knee" in the LF slope just about z>3. Figures are also presented at the end of this paper.

http://arxiv.org/abs/astro-ph/0601434

Nereid

Perhaps the one that kicked the idea you have off is this:
A Snapshot Survey for Gravitational Lenses Among z>=4.0 Quasars: I. The z>5.7 Sample

The "Richards et al. 2005b" in Strauss' Supporting Material, cited on slide 54 (and indirectly elsewhere?), seems to refer to:
A Snapshot Survey for Gravitational Lenses Among z>=4.0 Quasars: II. Constraints on the 4.0<z<4.5 Quasar Population (the preprint is 2005, the paper is 2006).

This is also pertinent to the question of lensing, but now rather old:
Imaging of SDSS z > 6 Quasar Fields: Gravitational Lensing, Companion Galaxies, and the Host Dark Matter Halos

It seems that lensing is only important, in Strauss' presentation, because it can introduce a 'magnification bias' into the observed quasar luminosities, and thus complicate the effort to estimate the quasar LF. In Strauss' presentation, no comments are made (that I could find) regarding what was expected. Further, the first two papers make it pretty clear that the then observed (lack of) strongly lensed quasars is not considered a test of LCDM models.

So, another of turbo-1's points bites the dust ... there seems to be nothing (in Strauss' video) re lensing "that should give any loyal BB-adherent pause"!

But maybe you had something else in mind, turbo-1? If so, would you care to share it?

= = = = = = = = = = = = = = = =

To turbo-1's more general point (which effectively encompasses all but the LF slope at z>3 one), and directly addressing the 'how can such massive AGNs form, with ~solar metallicities, at z~6.5?' I found this (bold added):

Formation of z ~ 6 quasars from hierarchical galaxy mergers:
Care to comment, turbo-1?

Nereid

Including, presumably, any "spatially and temporally infinite universe" models.

But I'm curious - what makes "a soaring LF at z>3" an essentially LCDM cosmological puzzle, to take just one of your points?

More generally, in your view, when does a puzzle in astronomy cease to be essentially an LCDM cosmological one?

That may be so.

However, does this make modern cosmology any different from any other part of modern science?

In any case, it's good to have you on record with this as your 'gold standard'. If (when?) any "spatially and temporally infinite universe" models get published, may we rely upon you to insist that any "puzzles (anomalous observations)" (with such models) be tackled (and solved) simultaneously?

May we also expect you to be highly critical of any "spatially and temporally infinite universe" models which contain "many adjustable parameters [] that can be tweaked to "allow" the fitting of one observation or another"?

OK, that's good to know.

I look forward to reading your next paper.

As I pointed out above, there have been successful predictions (e.g. Gunn-Peterson trough).

IIRC, the LCDM models have rather few free parameters - perhaps we could look at a recent paper, say one of the ones from the WMAP team?

Indeed it might.

Or it might not ... speculation can certainly be fun, but I'm sure you agree that it's not science.

Nereid

It simply means that Nereid was once a (Super) Mentor (more than once, in fact), but no longer has such a role in PF.

(more later; a most enjoyable post oldman!)

Nereid

Good idea.

I'll go listen to what Strauss actually said (in the video), and write a transcript (FWIW, I think, again, your summary is either too brief or has missed something vital wrt your claims).

Then I'll check what the paper that this presentation is largely from actually says (and I'd really appreciate it if you were to do the same ... PF's guidelines are pretty unambiguous about what sources should be used in threads like this ...).

After that I'll address the rest of this post, starting (perhaps) with a repetition of what's been covered already (about the origin of Fe etc); I'd appreciate it if you would review the relevant posts by me and matt.o on this topic, as this post of yours seems to have ignored them.

Nereid

The LF (luminosity function) is the (2D) relationship between intrinsic luminosity and volume density; crudely, how many quasars are there, per cubic Mpc (megaparsec), in the intrinsic luminosity range [M_i, M_i+1], over all M_i? In the Strauss video (and paper that it largely comes from), the vertical axis is logarithmic in Mpc^-3 mag^-1, and goes from ~10^-9 to ~10^-6 (for z>2 quasars). The horizontal axis (absolute magnitude, representing luminosity) goes from ~-24 to ~-29 (or perhaps -30).

(if you'd like a quick tutorial on 'magnitude', 'luminosity', etc, just holler)

For quasars, the current paradigm is to fit them with 'a broken power law', meaning that on the graph/plot/chart I have described, fitting two straight lines, one for the high-luminosity objects, and one of the lower luminosity objects, with a break-point (where the two line intersect). For the quasars under discussion here (those with z>3, and observed in SDSS DR3), the fainter-luminosity line is not so relevant.

The slope of the LF line (for higher-luminosities) is estimated by making a fit to the datapoints (in some statistical sense); such estimates are made (in the Strauss video) at z = 2.01, 2.40, 2.80, 3.25, 3.75, 4.25, and 4.75, by some binning of the data. Formal (1σ) error bars are calculated. When the fitted slopes are plotted, against z, they show a (z) trend, from ~-3.2 (z<3) to ~-2.1 (z=4.25), with the datapoint at z = 4.75 as an outlier (and with huge error bars). For z<3, the fitted slopes have values ~-3, with some scatter, but more or less within the error bars.

And that's it.

Perhaps you'd be interested in what astronomers interpret this set of (very substantially processed) material means?

If so - or if any other reader is interested - I'd be happy to try to explain ...