Arp objects, QSOs, Statistics

[Reality Check]

Is the sticking point here the empirical evidence for dark matter, or the mass fraction of said dark matter?

Not to mention the type of dark matter.

If I recall, the Quasi-Steady-State Cosmology model recognizes that there must be some baryonic dark matter existing, everywhere.

Don't QSSC or Plasma Cosmology adherents have a problem with the hugh mass fractions of the will-o-wisp non-baryonic CDM that standard cosmology hangs it's hat on?

I think even TeVeS and MOND predictions are for sizable mass fractions of dark matter in clusters like the Bullet. Just not the large quantities of the non-baryonic stuff.

The sticking point is that BeAChooser does not believe in the existence of dark matter at all. I do not know if he is a QSSC or Plasma Cosmology adherent (the latter looks likely). He calls dark matter a "gnome" added to Big Bang cosmology. When I first brought up the Bullet Cluster and the observation of dark matter there he said it was wrong because of a "host of gnomes".

The first (and only so far) gnome that he came up with is doubts about redshifts as described in this thread (so maybe I am not that far off-topic).
But the Bullet Cluster observation is about the relative masses between the gas in the galactic cluster detected via X-rays and the dark matter detected using gravitation lensing. The distance to the cluster is not an issue.

Since then BeAChooser has been strangely silent on this topic. If he cannot come up with something more then I will have to assume that he now accepts the existence of dark matter and the incorrectness of plasma cosmology.

 

[Dancing David]

And therein lies part of your problem, David. But I lack the interest to correct your misunderstanding of the problem.

How am I not suprised. Whatever. Fare thee well BAC

Don't tell us you work for a pollster?

My profile has always refelected my employment.

research in college, research into prevalence and barriers to treatment in mental health and homeless surveys. (Talk about some whinging, man the need to not duplicate surveys really bothers some people.)



In a while crocodile!

 

[Dancing David]

Help a noob out.............

Trolls are what they are, the most famous on this forum was Jedi Knight, the main strategy of a troll is to just get a response out of you , as in trolling when you are fishing. The are usually not interested in actual discussion but just counting coup in some way. They will ignore any pointed questions and engage in a wide variety of behaviors to avoid answering and making it look as though they are. Trolls mainly just want to spread thier nonsense and that is about it.

Some people look like trools but aren't they are cynics who are just contrarian, like Robinson, whose sarcasm runs deep and wide, he is not a troll, he just is very sarcastic at times.

Take a look at the Patterson-Gimlin thread in the General Sceptcism is you want to see some classic trolling.

 

[Dancing David]

Psst... this is a thread meant to be about Arp, statistics, please take your darm matter to where it belongs.

Trolling also involves the incessant moving of threads, so that they can be active but avoid questions.

 

[Wangler]

Alright already!

Back on topic:

So, are we coming to the following conclusions here:

1) It seems as if a posteriori statistics are used in astronomy perhaps more often than in other technical fields.

2) If we all acknowledge 1), it does seem as if Arp and others who author papers regarding "Arpian" theories are not as rigorous as some of their peers in their application of statistics of any type.

3) With 2) being stated, there are some apparently unique associations between some QSOs and some bright galaxies.

4) The only way to definitively prove that the associations mentioned in 3) are physical, or "Arpian", is to conduct further research, through actual observation or perhaps data mining of sources such as SDSS, etc. This research should be exhaustive in it's sample set selection, and multiple statistical tests should be made.

5) If the work in 4) could be performed, by a knowledgable and dedicated person, there might be a revolution in modern day cosmology in a pot at the end of the rainbow. Or, their might just happen to be a preponderance of universal "gotchas". And Arp is lucky to have found a bunch.

Does anyone agree with some, all or none of these points?

See, I can post on topic!

 

[DeiRenDopa]

Back on topic:

So, are we coming to the following conclusions here:

1) It seems as if a posteriori statistics are used in astronomy perhaps more often than in other technical fields.

2) If we all acknowledge 1), it does seem as if Arp and others who author papers regarding "Arpian" theories are not as rigorous as some of their peers in their application of statistics of any type.

3) With 2) being stated, there are some apparently unique associations between some QSOs and some bright galaxies.

4) The only way to definitively prove that the associations mentioned in 3) are physical, or "Arpian", is to conduct further research, through actual observation or perhaps data mining of sources such as SDSS, etc. This research should be exhaustive in it's sample set selection, and multiple statistical tests should be made.

5) If the work in 4) could be performed, by a knowledgable and dedicated person, there might be a revolution in modern day cosmology in a pot at the end of the rainbow. Or, their might just happen to be a preponderance of universal "gotchas". And Arp is lucky to have found a bunch.

Does anyone agree with some, all or none of these points?

See, I can post on topic!

.

Now here is an interesting set of questions!

However, if we're talking about astronomy and astrophysics, as branches of science, then 1) starts too far from the beginning to be of much help, and so the rest become not so interesting ...

In any case, 3) does not depend on 1) or 2) ... and unless it is much, much more tightly qualified is so boringly, obviously true that we need not waste any more time on it. Of course, every 'association' between any set of quasars and any set of galaxies (whether bright or not) is unique! What I think you may have intended to say is something about a general pattern, a relationship between a tightly defined subset of quasars and galaxies. This pattern could be something derived from a theory, such as the non-existent one BAC refers to, or simply something empirical, such as was the Hubble relationship in its first decade or so.

That leads to 4): one of the most common methods used in these two sciences (and, no doubt, in many others) is hypothesis formation and testing. It's not a free-for-all; there is centuries of bitter experience behind the 'guidelines' for doing this. In this thread there are, I feel, quite a few examples of misuse of this method (or failure to use it at all, or ...). In any case, your best chance of moving forward, with 4), is to develop a couple of hypotheses and go test them. One could be derived from 'theory', such as the Arp-Narlikar VMH, the other from a careful statement of an empirical relationship.

However, the whole chain (above) can be short-circuited by asking two, very simple, questions:

a) what is a 'quasar'?

b) are 'quasars' a homogeneous class of objects?

At some point, I hope, we will start discussing the former; the latter has already been discussed, and the Arp et al. idea has been shown, rather convincingly, to be inconsistent with thousands of observations.

 

[DeiRenDopa]

A series of posts on questions that remain unanswered.

In the next few posts I will re-post some questions that I have asked that do not seem to have been answered. It is entirely possible that they were and that I overlooked the answer(s); if so, I'd be grateful if someone could point to the post(s) which contain the answers, and also please accept my apologies in advance for not having found them myself.
----------------------------------------------------------
BAC: And just because Bell used a source that said it wasn't a complete list of all objects doesn't necessarily invalidate the results. Perhaps the objects in that list were a somewhat fair sampling of the overall population of such objects.

DRD: Perhaps they were; perhaps they weren't ... how do you evaluate the extent to which they were?

The context is a Bell paper which concludes that 'quasars' (Bell actually defines these quite clearly) are not at the cosmological distances their redshifts imply (from some form of the Hubble relationship). Central to the logic of Bell's paper is that VCVcat contains a set of 'quasars' that is complete in a well-defined, tightly constrained, sense. However, VCVcat is not such a catalogue. Here is the source post of my unanswered question.

 

[DeiRenDopa]

Second unanswered question: how does one go about evaluating material such as that in the various Arp et al. papers BAC has cited?

This is a slight paraphrase of the original, which can be found here.

 

[DeiRenDopa]

This isn't so much an unanswered question as a follow-up one.

How - specifically, quantitatively, within the estimated uncertainties - does an Arpian idea account for the full set of data for the 16 quasars [in a paper cited earlier] (and the existence of ~100 strongly lensed quasars)?

Where is the 'alternative cosmology' account of these results [strongly lensed quasars]?

(source)

Here is BAC's answer: No idea. Maybe Arp, et. al. will try to write one soon.

My follow-on question is: if at least some quasars have been shown, quite convincingly, to be at distances consistent with estimates derived from the Hubble relationship and their redshifts, and if there is no 'alternative cosmology' (or similar) which can account for these results/observations, what is to be gained, in terms of doing science, by a posterori analyses of highly selective quasar-galaxy alignments?

This question can also be asked in a slightly different form, using "well-formulated, quantitative, testable hypotheses" instead of 'alternative cosmology'.

Note that these questions are specific/concrete forms of more general ones about how astronomy and astrophysics, as sciences, are done.

 

[Dancing David]

Oooo, I have a side bar here in this thread at this post and it is related to the appearance of associations
http://www.internationalskeptics.com/forums/showpost.php?p=3604593&postcount=183

we have a picture of a galaxy and under the picture we have
"What leads you to believe that region is "transparent"? After all, I linked peer reviewed scientific papers by astronomers who conclude it is not. Astronomers who concluded the quasar was almost certainly on this side of NGC 7319 and part of their reasoning was the likely density of obscuring matter. For example, http://www.journals.uchicago.edu/doi...10.1086/426886 states "there are no signs of background objects showing through the disk in our HST picture of the inner regions of NGC 7319"."

Now I am not saying that there are not people who made this statement but that picture contains an 'artifact of exposure' which is ignored in this argument. I would characterize this three ways (by the poster) an appeal to common sense/intuition, a lack of understanding of artifact (which the authors might be guilty of) and what I call 'it looks like a bunny'.

The first and third go together and they are based upon the second, an artifact of exposure.

To gather pictures and discern possible structures long exposure times are used. this has a number of effects it creates a larger burn area around fore ground objects, often obscuring features, it great a look of solidity and opaqueness that may not be there, it brings out the structure of detail objects (but not the objects themselves unless the resolution is high enough), it allows very faint sparse structures to become more apparent.

Here you can see a picture made by the VLT where there is this blurring and hazy effect from the exposure, caused by scattering amongst other things.
http://antwrp.gsfc.nasa.gov/apod/ap011021.html

here is one that due to resolution is even more apparent what blurring by exposure can look like (it is down at the bottom) also look there is a blue ring.
http://images.google.com/imgres?img...brero+galaxy&start=20&ndsp=20&um=1&hl=en&sa=N

and here is one where the effect is compensated for but is still there to some extent
http://antwrp.gsfc.nasa.gov/apod/ap080308.html

Now you will note the prominent bulge is not there in the third picture and that other objects are more visible (although they are foreground objects by and large)

So when the poster makes the statement and provides the statement by the authors what is it doing:

1. Common sense says that in this picture there is a solid area of white something, the poster ignores the artifact and the say ‘it looks like a bunny’, therefore it is a white something that is opaque.

Now I am very curious how the authors came to the conclusion that background objects were not visible , due to this artifact?

 

[DeiRenDopa]

VCVcat and what's a quasar - appearance and reality?

Perhaps part of what's involved in discussion of VCVcat and its uses is the difference between the surface reality (appearance) and the deeper one.

Briefly, if for Bell's conclusions to hold his selection of objects from VCVcat needed to be an unbiassed sample of some population, then we can say with near certainty that those conclusions do not follow, logically, from his assumptions ... because the objects he selected from VCVcat are certainly not an unbiassed sample (and he did not, it seems, attempt to estimate the bias).

This holds no matter what words of caution the authors of VCVcat wrote in their intro, as one could determine for oneself by looking up the sources the authors used for the objects Bell selected.

Of course, the authors did, in fact, explain how their catalogue was compiled, and they also did warn that it should not be used for statistical analyses ... so the appearance closely matches the reality anyway.

Maybe it's time to look at what a 'quasar' is?

 

[DeiRenDopa]

While you clearly have put a lot of work into this BeAChooser, I'm sorry to say that it is full of mistakes, of many different kinds.

For those mistakes which are attributable to textbook statistics, may I suggest that an investment of your time in a formal course, or in a good textbook, would be worthwhile?

For the rest of my post, I will focus on the astronomy, and how you have set up your (statistics, arithmetic, etc) problems incorrectly, not on the inner workings of the stats (etc).

Wrong. The paper I cited on NGC 3516 (http://www.journals.uchicago.edu/doi/abs/10.1086/305779 ) talks about 5 quasars along the minor axis. The object at z = 0.089 is identified this way: "there is a very strong X-ray source that is listed as having a Seyfert spectrum (Veron-Cetty & Veron 1996) with redshift z = 0.089 (about 10 times the redshift of NGC 3516). Optically it is a compact, semistellar object. With its strong X-ray and radio properties, it is closely allied to BL Lac objects and therefore to the transition between quasars and objects with increasing components of stellar populations."

.
I already covered this, a bit, in an earlier post; I will address this in much more detail when I discuss "what is a quasar?".

Suffice it to say that how this question is answered is critical to evaluating the kinds of calculation/estimates commonly found in Arpian papers (and in this post of yours I'm quoting).
.

Except that two (of six) quasars do not match the predicted z within 0.1

True, but I was trying to simplify the problem by balancing the fact that 3 (of the five) fall into intervals less than 0.10 in width. But since you apparently aren't satisfied with my simplification, let's take another look at the whole problem.

Let's start by matching each observation with it's corresponding Karlsson value: (0.33,0.30) (0.69,0.60) (0.93,0.96) (1.40,1.41) (2.10,1.96). That means the distance from the Karlsson value in each case is 0.03, 0.09, 0.03, 0.01, 0.14 , respectively. To compare with the 0.10 discretization I used in my calculation, we must double those values: 0.06, 0.18, 0.06, 0.02, 0.28 . Note that 3 (of five) fall within a 0.06 discretization but you are correct that 2 don't fall within a 0.10 interval.

Let's redo the calculation for just those three cases and see what we get, assuming again that the quasars randomly came from a population with an equal distribution of probability between 0 and 3.0. There are 50 possible values in that range given an increment of 0.06. Now looking at this again, I don't think I should have used the permutation formula in the previous calculation. This time let's just use the combination formula ... in other words, let's find the number of possible combinations of those those r values from n possible values.

The formula for that is n!/((n-r)!r!). Thus the probability of seeing those 3 values turn up is 1/(n!/((n-r)!r!). In this case, that works out to 1/(50*49*48/3*2) = 5.1 x 10^-5.

And now let's factor in the unlikelihood that we'd find 2 more quasars near that galaxy that are unusually close to the Karlsson (K) values of 0.60, and 1.96. Surely a conservative estimate for that probability would be to simply find the chance of each specific number turning up given an increment appropriate for that case. For the 0.69 case, for example, where the increment is 0.18 (twice the 0.09) value, over the range 0 to 3.0, there are at least 16 increments. So, the probability of finding that number 1/16 = 0.06. For the 1.96 case, the increment needs to be 0.28 and there are 10 possible values. The probability is 1/10 = 0.10. And finding these z's should be relatively independent of finding the others, so the probabilities should simply multiply together to give a final combined probability.

Therefore, I assert that, to a first order, the probability from the 3 number sequence can be adjusted to account for the unlikelihood of the 2 other quasars by multiplying it by 0.06 * 0.1. And that results in a final combined probability of 5.1 x 10^-5 * 0.06 * 0.10 = 3.06 x 10^-7. So to a first order, it appears my initial assumption that an increment of 0.1 used for all of them would balance everything out off by a factor of about 10.

(bolding added)

Here are some, just some, of the considerations not included in the above:

* how was NGC 3516 selected? We know, from the Chu et al. paper, that it was most certainly not a random selection!

* how many 'near NGC 3516 quasars' were known before Chu et al. planned their observations? before Arp chose to look at the field around NGC 3516 again? We know, from the Chu et al. paper, that there was at least one ("One of the objects, Q1107]7232 (C\7.1), is already listed in the Hewitt-Burbidge (1993) quasar catalog.")

* how are quasar redshifts distributed, in [0,3]? If they are not distributed equally (to within some bound), then probability calculations need to reflect that non-equal distribution

* your calculation, on its own, would seem to apply to any set of three numbers in [0,3]; you have calculated the a posterori probability, and not addressed sol invictus' comment (in another thread)

.

And lest you think the selection of z = 3.0 as the upper bound in my calculation is arbitrary, let me note that I found a mainstream source that said, based on the SDSS study, the number of quasars decreases by a factor of 40 to 50 from z = 2.5 to z = 6.0. Therefore, I think I am justified in using a range of z = 0 - 3.0 in my calculations for quasar z. I will agree that the density of quasars of different z is not uniform over the range. Several of the sources I found indicated that it climbs rather steeply from a value at z = 0 to z = 1.5 and then levels off through z = 3.0. I don't see an easy way to incorporate this fact into the calculation but I don't think it really makes much of a difference since the differences between the Karlsson values and the observed z don't appear to have much of a trend up or down over the range.

.
As I noted earlier, if the range is [0,3], then all the Karlsson values in that range need to be included.
.

However, since you questioned my 0.10 simplification, I'm going to take another look at the rest of the calculation, starting with what I estimated was the total number of quasars in the sky. Recall that I estimated the total number of quasars that can be seen as 1,237,500 ... by multiplying the number of square degrees in the sky (41,250) by 30 quasars per square degree. But is 30 quasars per square degree really a reasonable value to use?

Here's a 2005 study http://www.iop.org/EJ/abstract/1538-3881/129/5/204 that indicates an average density of 8.25 deg^-2 based on the SDSS survey then argues it should be corrected upward to 10.2 deg^-2 to make it complete. And if you go to the SDSS website (http://www.sdss.jhu.edu/ ) you find they say the effort will observe 100,000 quasars over a 10,000 deg² area. That also works out to about 10 quasars deg^-2. So it looks like I used a number that was 3 times too large in my earlier calculation. In this revised calculation, I will only assume the average quasar density is 10 deg^-2. That means the total number of quasars than can be seen from earth is around 410,000.

.
The Chu et al. paper carefully explains how they chose which objects to observe (in order to measure redshifts); the "average density" of quasars you need to use in this part of your calculation is that which would be obtained if the search method used in Chu et al. were to be used over the whole sky. As there appears to be no effort to explain this, in any quantitative fashion, let alone estimate it, you are left with an unknown.

It might be possible to estimate bounds on this, but without any such attempt, you have no basis for this calculation at all.

Oh, and as I explained in a reply to Wrangler earlier, in any case, you need at least a measure of the variation in average density (as well as the average density), to make the sorts of estimates this part of calculation aims to do.
.

So now we come to the question of how those 410,000 quasars are distributed, or more precisely, how many galaxies with 5 or more quasars near them can be expected in the total population of galaxies that can be seen. Now recall that in my previous calculation I initially assumed that the all the quasars are located near galaxies and distributed 5 per galaxy until the number of quasars available is exhausted. That resulted in an estimate of 250,000 (~ 1,237,500 /5) galaxies with 5 quasars each. Doing that maximized the total number of galaxies assumed to have 5 quasars which was a conservative approach from the standpoint of not wanting to over estimate the improbability of the observation of NGC 3516.

But the truth is that most quasars do not lie close to galaxies at all (certainly not galaxies where we can discern any detail as is the case in all three examples of interest here) so that's why I later multiplied the calculated probability by 0.10 to account for the assumption that only 10% of quasars lie next to a galaxy. I still think that's probably a reasonable number. But for this calculation, I'm going to give your side the benefit of the doubt and assume that fully half of all quasars are near galaxies. That has to be very conservative. Wouldn't you agree. So now there are 205,000 in the population that we need to distribute amongst galaxies.

.
Making up numbers, and using one's intuition about what's conservative, reasonable, etc, in astronomy is an almost certain way to be wrong.

There are many approaches to choose from, when it comes to determining robust bounds/estimates; they all involve much greater use of the hard-won data astronomers have gathered these past century or three than the approach above.

One modern method is a Monte Carlo simulation; one reason it's popular is that it can test models that have a range of input parameters, and they can avoid the need to work through the intermediary steps.
.

It's also apparent that most galaxies that have nearby quasars only have a few quasars ... not 5 or more. I didn't find any source actually quantifying this but we can observe that in Arp's catalog of anomalous quasar/galaxy associations, relatively few of the examples have 5 or more quasars in the field. Therefore, I think it's conservative to assume that only half the quasars are in groups of 5 or more near galaxies. You would agree, right? In fact, I think this is very conservative assumption, otherwise Arp's list of anomalous quasar/galaxy associations would have likely contained far more examples with large numbers of quasars. In any case, I'm going to reduce the number of quasars available to comprise the population of galaxies that have 5 quasars by half ... to 103,000. Now if you divide that number by 5, that means there are at most 20,600 galaxies visible that have 5 quasars in their vicinity.

.
Earlier you introduced a paper by L-C&G, which presented some rather concrete numbers of just what you are trying to estimate; why not use what's in that paper?

In any case, an imporant error in your work is, as I have said, conflating what Arp, Chu, et al. found with what's reported in large surveys ... without going into the nitty-gritty of how comparable the methods of estimation are.

(to be continued)

PS NGC 3516 is outside the coverage area of SDSS DR6 (the latest), and it certainly was not observed in the 2dF survey! (this galaxy has a Dec of +72!)

 

[Wangler]

Here you can see a picture made by the VLT where there is this blurring and hazy effect from the exposure, caused by scattering amongst other things.
http://antwrp.gsfc.nasa.gov/apod/ap011021.html

DD, what blurring and haziness are you referring to? Are you talking about the extended halo around the Sombrero? Because, if you are, that is not an artifact, or blurring. That is the extended outer halo of stars around the galaxy. It is very pronounced, due to the high S/N of this image, and due to the non-linear contrast stretch used on this image. Make no mistake, though, the halo is made up of Sombrero stuff.

here is one that due to resolution is even more apparent what blurring by exposure can look like (it is down at the bottom) also look there is a blue ring.
http://images.google.com/imgres?img...brero+galaxy&start=20&ndsp=20&um=1&hl=en&sa=N

Again, there is no blurring here. Just a very high S/N ratio caused by the extended exposure time obtained for this image.

and here is one where the effect is compensated for but is still there to some extent
http://antwrp.gsfc.nasa.gov/apod/ap080308.html

The S/N on this image may not be as good, or it is also likely that the contrast was not as "stretched" as in the other image.

I don't think that there is any "effect" at work here, just the star-stuff associated with the galaxy. The only effect is the S/N in the image, and the amount of post-processing applied to the image.

Now I am very curious how the authors came to the conclusion that background objects were not visible , due to this artifact?

They simply state: "There are no signs of background objects showing through the disk in this HST picture
of the inner regions of NGC 7319".

They also go on to show absorption lines, and reddening of the QSO, both indicative of some sort of matter between us and the QSO.

Spiral galaxies are not that dense in their rotational plane, even this close to the nucleus.

Why wasn't a spectrum taken of the stellar object just to the lower right of the QSO. It may be a foreground star, but maybe it is not?

I think that the evidence I see points to the QSO being at the distance indicated by it's redshift.

 

[Dancing David]

Okay, so I am wrong. Figures.

I will state it for the lurkers, I was wrong.

I really thought there was some scattering and blurring going on. But if it is the single stars showing because of long exposure that is even cooler.

I guess I am old fashioned, thinking like film and the foreground tars burning into the picture.

Sigh, I remember when we only had a balck and white TV. And no microwave.

 

[BeAChooser]

Bill Keel did an extensive study of the optical depth of the arms of (bright, big) spiral galaxies, using some pretty clever methods.

He concluded, in a series of papers on this topic, that it is rare to find any part of any arm of a spiral that has an optical depth of >1.

Too bad you didn't see fit to provide us with a link to those papers. But that's ok ... I found Keel's papers. And now I know why you didn't. Because they show you either misinterpreted Keel's conclusions or you are misrepresenting them.

The story starts with the findings of Edwin Valentijn back in 1990: http://findarticles.com/p/articles/mi_m1200/is_n2_v138/ai_9221687 "Casting shadows on spiral galaxies, Science News, *July 14, 1990 *by Ivars Peterson ... Reporting in the July 12 NATURE, Edwin A. Valentijn of the Kapteyn Astronomical Institute in Groningen, the Netherlands, suggests that major parts of most spiral galaxies are heavily clogged with light-absorbing dust. In many cases, the dust enshrouding the inner parts of a galaxy appears so thick that astronomers actually see only the outer crust of stars. ... snip ... The old view that spiral galaxies are largely transparent arose from studies of how the average surface brightness of galaxies differs depending on whether an observer sees a galaxy face-on or tipped at an angle. Dust-free, transparent galaxies would have comparable luminosities when viewed from any direction, whereas dust-clogged galaxies would look brightest observed face-on. Valentijn originally set out to determine what factors may have biased the original studies of spiral-galaxy transparency. His precise measurements of the brightness of more than 12,000 carefully selected spiral galaxies revealed that these galaxies appear much more opaque than earlier studies had indicated. "I was very surprised because the results contradicted many famous papers in this area," Valentijn says."

In 1998, William Keel and Raymond White published this: http://www.astr.ua.edu/keel/research/aasdust.html "COSMIC SILHOUETTES GIVE RARE GLIMPSE OF GALAXIES' DUST ... snip ... The investigators presented images ... snip ... of two striking pairs of galaxies, each with a spiral galaxy in front of a smooth elliptical companion. ... snip ... the astronomers did see what they expected to find, that the dust is patchy and clumped, largely aligned along the spiral arms. "Having most of the absorbing dust in the spiral arms, where most of the light originates, is what caused the statistical studies to wrongly conclude that spirals are opaque," says White." And while that report states "The dustiest patches that appear in the HST images aren't very dark, since at least 20% of the blue light comes through, and even more of the near-infrared light," the foreground galaxy has little similarity to the NGC 7319. NGC 7319 looks like this:

http://ucsdnews.ucsd.edu/graphics/images/2004/spiralgalaxy.new.gif

The foreground galaxies (AM1316-241 and AM0500-620) studied in this paper look like this:

http://apod.nasa.gov/apod/image/9801/am1316_hst.jpg

and

http://www.smv.org/hastings/350kbg.jpg

As you can see, they weren't looking through material anywhere near the core of the foreground galaxies.

In fact, this Keel paper goes on to say "These galaxy pairs only tell us about their outer regions, where the backlighting is strongest; the inner parts of galaxies, richest in heavy chemical elements and perhaps in dust, are much more difficult to explore."

Now of course, the series of papers you were probably refering to are the ones titled "SEEING GALAXIES THROUGH THICK AND THIN", of which this is the first paper:

http://www.journals.uchicago.edu/cgi-bin/resolve?ApJ35086PDF "SEEING GALAXIES THROUGH THICK AND THIN. I. OPTICAL OPACITY MEASURES IN OVERLAPPING GALAXIES, Raymond E. White III, William C. Keel and Christopher J. Conselice, THE ASTROPHYSICAL JOURNAL, 542: 761-778, 2000 October 20" .

And here is what this paper actually says about opacity:

"Even though typical spirals are not optically thick throughout their disks, where they are optically thick is correlated with where they are most luminous: in spiral arms and inner disks. This correlation between absorption and emission regions may account for their apparent surface brightness being only mildly dependent on inclination, erroneously indicating that spirals are generally optically thick. (BAC - DRD, this last statement is what Keel et. al. were actually arguing against, not your claim that spiral arms are not optically deep.) Taken as an ensemble, the opacities of spiral galaxies may be just great enough to significantly affect QSO counts, though not enough to cause their high redshift cutoff. ... snip ... In the following discussion of individual objects, we will tend to quote magnitudes of extinction A rather than optical depths Tau, where A = 1.086Tau. ... snip ... As reported in White & Keel (1992), our best case thus far is AM1316-241, an Arp-Madore catalog object consisting of a foreground Sbc projected against a background elliptical. ... snip ... The opacity is clearly concentrated in the spiral arm, while the interarm region is nearly transparent. ... snip ... The E/Sbc pair AM 0500-620 shares some of the favorable characteristics of AM 1316-241 — it is comprised of a relatively undisturbed foreground spiral and a symmetric background elliptical ... snip ... along the arm ridge line, we find A_B > 3.0 and A_I = 2.1, while the interarm extinction ranges over A_B = 0.1 - 0.6 and A_I = 0 - 0.7 at various points seen against the elliptical ... snip ... The Sbc pair NGC 4567/8 (UGC 7777/6) is another case where the analysis is limited by the general lack of symmetry ... snip ... Here we concentrate on the dark lane in the upper left of Fig. 5a which cuts across a brighter background galaxy arm. ... snip ... We calculate face-on extinctions of A_B = 1.1 and A_I = 0.69 for this region ... snip ... This somewhat strengthens our interpretation of the excess light as indeed shining through a more transparent interarm medium. ... snip ... UGC 2942/3 This is a pair of highly-inclined spirals, with the background galaxy seen only a few degrees from edge-on ... snip ... To estimate the extinction in the foreground spiral UGC 2942, we consider intensity slices perpendicular to the projected plane of the background galaxy UGC 2943. ... snip ... The implied optical depth across the spiral arm (within the dust lane) is of order Tau_B = 3. ... snip ... NGC 3314 NGC 3314, a remarkable superposition of two spirals in the Hydra cluster (Abell 1060), was considered in the context of opacity measurements by Keel (1983). ... snip ... this system is uniquely valuable because we can estimate extinctions in the foreground galaxy closer to its center than in any other of our sample. ... snip ... The best places for reliable extinction measurements are the points where the arms of NGC 3314a cross the disk edges of NGC 3314b, going from projection against the bright disk to projection against almost blank space at essentially the same radial distance for the arm. We measured the arm intensities at adjacent points on and off the background disk, after subtracted a minimal exponential-disk model to flatten most of the background gradient (so that interpolation to get the relevant unobscured background intensity is better constrained). For two locations where the arms cross the disk at about 0.5R₂₅, both A_B and A_I are comparable at 1.8, while the interarm regions average A_B = 0.60 and A_I = 0.34. ... snip ... Summary and Discussion We have presented absolute extinction measures for 11 spiral galaxies in overlapping pairs. For each pair, there is some range of radii for which we can measure the residual intensity of background light transmitted through the foreground disk. We translate these measures into arm and interarm extinctions (where such a distinction is possible) in both B and I bands. In almost all cases, there is a large difference between arm and interarm values. In arm regions, A_B ~ 0.3 - 2 and A_I ~ 0.15 - 1.4[/b], while in interarm regions, A_B ~ 0.07 - 1.4 and A_I ~ 0.05 - 1.3. ... snip ... The arm and interarm plots are drawn to the same scale to emphasize that arm regions tend to be much more opaque than interarm regions. ... snip ... The interarm (“disk”) extinction tends to decline with radius (Fig. 12b) from A_B values of only ~ 1 magnitude within ~ 0.3R₂₅ . In contrast, spiral arms and resonance rings can be optically thick at almost any galactocentric radius. ... snip ... Our initial results on AM1316-241 (White & Keel 1992) led us to conclude that disk opacity is concentrated in spiral arms and that interarm regions are fairly transparent. Our newer work is generally consistent with this picture, with resonance rings found to be as optically thick as spiral arms. Therefore, the distribution of absorption tends to be spatially correlated with particularly bright regions, since spiral arms are brighter than interarm regions. We suggested (White & Keel 1992) that this spatial correlation between internal extinction and emission may account for the statistical results reported in earlier studies — that surface brightness is roughly independent of inclination. The dust is optimally placed to affect global blue photometric properties, since typically half the disk light comes from only about 20% of its area, accounting for the rather flat inclination-surface brightness relation, without requiring galaxies to be optically thick in interarm regions. ... snip ... Since our measurements are based on spatially averaged transmission values, the “effective” extinction may not be fully comparable to the extinction curves derived from what are essentially point sources in our own and nearby galaxies. ... snip ... Our results bear on the question of whether the high-redshift “QSO cutoff” can be produced by absorption in spirals along the line of sight. ... snip ... For a fiducial set of spiral galaxy parameters, Ostriker & Heisler (1984) estimate that 50% of QSOs at z = 4.5 will suffer such obscuration by foreground galaxies; this is close enough to the characteristic peak redshift in the QSO distribution at z ~ 2.2 to make obscuration effects worth investigating. We find that disks are optically thin in spiral types Sb and later, which have A_B < 1 from 0.5 to 0.9 R₂₅; extinctions are below our measurement errors for R > R₂₅. The typical interarm behavior of our sample is very close to the model adopted by Ostriker & Heisler (1984), except that we find extinctions (at B) less than they assume by factors always greater than 2. Their fiducial model is based on the radial structure of the Milky Way and the integrated extinction perpendicular to its disk at the solar location R ... snip ... This implies that the Ostriker & Heisler model has A_B = 0.9 at 0.5R₂₅, in contrast to the A_B = 0.1-0.4 values we find for interarm regions at similar radii. Spiral arms will provide additional absorption, but they cover rather less than half the surface area in grand-design spiral disks. The covering fraction of spiral arms tends to be larger in flocculent spiral galaxies, however. ... snip ... While detailed calculations of this effect based on local galaxies may not be relevant to the high-z objects responsible for most of the cumulative extinction, we do note that a two-component model treating arm and interarm regions separately should reflect local reality much better than a single-zone scheme ; most spiral arms are opaque enough to drop a QSO out of observed samples, but the half (or more) of a disk between dusty arms remains usefully transparent over much of the disk's projected area..

And in case you missed what is stated by Keel above, the magnitude of extinction, A, equals 1.086 times the optical depth. Thus, if A > 1.086, the optical depth is greater than 1. So numerous examples are provided above where in the arms of the spirals the optical depth is greater than 1, even much greater than one. And based on the number of such examples in the above paper out of all the cases it examines, one would have to conclude finding optical depths greater than 1 in the arms of spirals near the core is NOT a rare thing at all. So you see, DRD, they did not conclude what you claim they did. If fact, I don't think you even read the paper. Is that how you typically conduct your research? Or were you just too busy working on your study of trolls and their effect on thread length to read it?

And note that the case they said was "uniquely valuable because we can estimate extinctions in the foreground galaxy closer to its center than in any other of our sample. looks like this:

http://www.utahskies.org/image_library/deepsky/ngc/ngc3314.jpg

That foreground galaxy doesn't look anywhere near as dense as NGC 7319. I think you're hand-waving, DVD.

And here's what the fourth paper in Keel's series says:

http://www.astr.ua.edu/preprints/keel/index.html "Seeing Galaxies through Thick and Thin. IV. The Superimposed Spiral Galaxies of NGC 3314 by William C. Keel and Raymond E. White III, in press in the Astronomical Journal for September 2001." ... snip ... "Using a larger sample of 12 suitable backlit spirals, White, Keep, & Conselice (2000; WKC) found this to be representative behavior: arms and resonance rings can have substantial opacities (Tau_B at any radius ... snip ... In the innermost few hundred pc, even the most transparent regions between dust lanes show A_B ~ 7 and there are dusty arms with A_B > 8.2. "

Again, remember that A > 1.086 is an optical depth of 1.0, so it appears the arms near the core of spirals can be VERY opaque.

The Einstein Cross, or QSO 2237+0305, is a background quasar lensed by a foreground galaxy ... and it is 'seen' right through the densest part of ZW 2237+030.

Let's just show folks what that "supposed" foreground galaxy looks like in this case, shall we?

http://apod.nasa.gov/apod/image/0703/qso2237_wiyn.jpg

And note that the 4 components of the Cross are reportedly separated by 0.9 arc seconds. That compares to a separation of the NGC 7319 quasar from the core of 8 arc seconds. So the entire galaxy you see in your example has about the apparent radius of the distance from the nucleus of NGC 7319 to its quasar.

By the way, Arp claims that the Hubble Space Telescope images show connecting material between one of the quasars (D) and the central galaxy and a high redshift connection has also been discovered between quasars A and B, passing in front of the connection between the nucleus and quasar D. Plus, the brightness of the four quasars was observed to increase over a period of several years from 1991 to 1994. Arp's explanation is that the galaxy has ejected four quasars, which are growing brighter with age as they move farther from the nucleus.

And here's a paper, http://vela.astro.ulg.ac.be/themes/dataproc/deconv/articles/q2237/q2237.html#len , that concludes one quasar image's light is being absorbed and reradiated by dust ... which might be the case if the quasars are actually separate objects embedded in the host galaxy but unlikely in a lensing case. Chandra observations also indicate that object A has a broad emission line in the Fe/K alpha while objects B,C,D do not. How can this be with a single lensing galaxy? Afterall, according to NASA (http://hubblesite.org/newscenter/archive/releases/1995/43/text/ ), "it is impossible to identify the true gravitational lenses without observations which show the two objects have exactly the same spectral fingerprint and so are "multiple" images of a single object." Apparently, these don't.

Do you mind if I ask you how you go about evaluating the thousands of papers, written by hundreds (or more) of other astronomers, who find that quasars are at distances implied by their redshifts (per the Hubble relationship)?

Funny how these hundreds of astronomers have nothing to say in the case of NGC 7319. The silence is deafening.

 

[BeAChooser]

The sticking point is that BeAChooser does not believe in the existence of dark matter at all.

That's not true. I have no problem with baryonic dark matter. I've said that many times.

And it's because certain posters keep mischaracterizing what I actually said that I choose to ignore some of the efforts to debate me on certain threads after basically everything has been said that needs to be said and after I've been repeatedly insulted on those threads. So if I wish to discuss dark matter then I will visit that thread you mentioned. But I would appreciate your confining your remarks on this thread to the matter of redshift and observations that suggest redshift might not equate to distance in all objects. For example, would you like to comment on my calculation regarding the improbability of so many redshifts in quasars near certain galaxies that are close to the Karlsson values? Or do you have something to add regarding NGC 7319 and the quasar that appears to be on this side of it?

 

[Reality Check]

That's not true. I have no problem with baryonic dark matter. I've said that many times.

And it's because certain posters keep mischaracterizing what I actually said that I choose to ignore some of the efforts to debate me on certain threads after basically everything has been said that needs to be said and after I've been repeatedly insulted on those threads. So if I wish to discuss dark matter then I will visit that thread you mentioned. But I would appreciate your confining your remarks on this thread to the matter of redshift and observations that suggest redshift might not equate to distance in all objects. For example, would you like to comment on my calculation regarding the improbability of so many redshifts in quasars near certain galaxies that are close to the Karlsson values? Or do you have something to add regarding NGC 7319 and the quasar that appears to be on this side of it?

Then I must have misunderstood your "hosts of gnomes" objection to the dark matter observation in the Bullet Cluster. It was not referring to the dark matter, it was just the one gnome about the distance to the Bullet Cluster as measured by redshift.

I am not an expert in statistics but I will look at your calculation about "improbability of so many redshifts in quasars near certain galaxies that are close to the Karlsson values". It looks plausible at first glance but so many statistical calculations do and many posters seem to disagree with the calculation.

As for NGC 7319: The quasar looks as if it is shining through the galaxy. If all galaxies were opaque throughout their structure then this would mean that the quasar is in or in front of the galaxy. But galaxies are not solid so there is always the possibility that we are looking through a hole like the Lockman Hole. However it is unlikely to be in front of the galaxy since the Pasquale Galianni, et. al. paper states that the QSO spectrum has absorption lines in it consistent with the gas in the galaxy.
This is definitely not an issue that will be resolved in this forum. As the authors conclude:

More studies are required, since this is the only system found so far in which there is the possibility of demonstrating more clearly that the QSO and galaxy are interacting.

 

[Wangler]

And here's a paper, http://vela.astro.ulg.ac.be/themes/dataproc/deconv/articles/q2237/q2237.html#len , that concludes one quasar image's light is being absorbed and reradiated by dust ... which might be the case if the quasars are actually separate objects embedded in the host galaxy but unlikely in a lensing case.

I am not sure how you differentiate these two cases, BAC.

Why would different absorption be plausible for separate objects, but not plausible for lensed images?

The only way it is plausible for separate objects is if they are in differing areas of opacity.

The same difference in opacity would also be reflected in the lensed images.

 

[DeiRenDopa]

Just a quick note to thank BAC for the lengthy reply, to say that it's good to see Reality Check, DD, and Wrangler beginning to engage BAC on the specifics, and that I may not be able to post for a couple of days or so ...

Also, if anyone is sufficiently interested, perhaps you'd like some suggestions on where to go to get more detailed, in-depth info on astronomy (etc), and a suggestion that I don't think this JREF forum is quite set up to cover parts of the issues and questions raised here ...

 

[Zeuzzz]

As for NGC 7319: The quasar looks as if it is shining through the galaxy.

One quick comment,,,

You may beable to pass off one as a mere co-incidence, but, for example, Galaxy NGC 7603 has two definate small quasar like objects clearly at both points in the plasma filament connecting the quasar to the galaxy. Both have very different Redshifts.

Theres a picture of it about twenty seconds into this documentary, with various astronomers talking about it;

http://www.youtube.com/watch?v=EjQVybreSUs