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folkhemmet
2007-Jul-04, 08:30 AM
Many baut forum viewers/members are probably aware of the debate over the implications of discordant redshifts. First of all, certain groups of a galaxies may have a member galaxy with a vastly different redshift than its neighbors. If it can be definitely proved that galaxies in the same group have vastly different redshifts, then the entire paradigm of an expanding Universe in which redshift and distance are intimately related would be called into serious question.

In some cases a galaxy with a discordant redshift may be smaller than the other galaxies and may just appear to be close to the lower redshift galaxy when in actuality it is a larger galaxy much further away. However, what about cases in which the galaxies are of very similar angular sizes and part of the same group AND they have discordant redshifts? Are there simpler more mundane explanations that don't involve novel physics that could explain a situation like this?

Nereid
2007-Jul-04, 01:12 PM
what about cases in which the galaxies are of very similar angular sizes and part of the same group AND they have discordant redshifts?Perhaps a different question, or set of questions, should be asked first?

Which cases? Which galaxies? How is group membership established? What are the redshifts?

For example, if there are two galaxies, and if they have an 'angular size' of tens of arcseconds (or more), then relevant observations may give a distribution of redshift across significant parts of the both galaxies.

BAUT member Bill Keel has studied many cases (http://www.astr.ua.edu/keel/research/dust.html) with similarities to your hypotheticals. Perhaps a good way to address the general question which your more restrictive OP is a part of would be to ask why the galaxies in Keel's studies have 'discordant' redshifts?

Cougar
2007-Jul-04, 05:20 PM
Those are good points by Nereid. I have some different points about the slant of your OP.


First of all, certain groups of a galaxies may have a member galaxy with a vastly different redshift than its neighbors.
Wait a minute. You're already calling it a "member galaxy." How do you know it's a member of the cluster, especially if it has a vastly different redshift?


If it can be definitely proved that galaxies in the same group have vastly different redshifts, then the entire paradigm of an expanding Universe in which redshift and distance are intimately related would be called into serious question.
Actually, no, I don't think so. There are too many observations confirming the redshift-distance relation. If, as you say, "it can be definitely proved that galaxies in the same group have vastly different redshifts," then rather than throwing out the whole idea of the expansion of the universe, I would think a solution more local to the anomalous phenomenon would be sought.


In some cases a galaxy with a discordant redshift may be smaller than the other galaxies and may just appear to be close to the lower redshift galaxy when in actuality it is a larger galaxy much further away.
That's right. Galaxies come in a wide variety of sizes, so unless you know how big your galaxy is supposed to be, you can't be sure of its distance - apart from its redshift indication.

However, what about cases in which the galaxies are of very similar angular sizes and part of the same group AND they have discordant redshifts?
The "very similar angular size" does not necessarily imply they're at the same distance. Again, how did you conclude they are "part of the same group"? Space is very deep. Some odd and remarkable alignments might be expected.

Tim Thompson
2007-Jul-04, 05:26 PM
Are there simpler more mundane explanations that don't involve novel physics that could explain a situation like this?
In general, yes. The measured redshift for any galaxy is the resultant of more than one simultaneous effect. One cause of reshift is the relative motion from the expansion of the universe. Another is the "local" motion of the galaxy, which is usually called the "peculiar" motion by astronomers. The closer a galaxy is to us, the more dominant is the peculiar motion, and the less important is the universal expansion.

The term "discordant" redshift is deceptive, because they are "discordant" only in the cosmological sense. If, for instance, one galaxy is passing through another group of galaxies, it will be travelling at a remarkably different velocity, and so will have a remarkably different redshift. But there is nothing "discordant" about it unless you assume that the redshift is entirely cosmological in origin. But that is not always a good assumption.

That should work in principle, although I don't know of a specific example. Both Stephan's Quintet (http://www.noao.edu/image_gallery/html/im0414.html) & Seyfert's Sextet (http://antwrp.gsfc.nasa.gov/apod/ap030124.html) are examples of chance alignments of galaxies at different distances. But it might be noted that in both of those cases, the angular size of the "discordant" galaxies are not obvious indications of different distances.

jamini
2007-Jul-04, 05:33 PM
If it can be definitely proved that galaxies in the same group have vastly different redshifts, then the entire paradigm of an expanding Universe in which redshift and distance are intimately related would be called into serious question.
Given our current technology, it is not likely that anything like this could be conclusively proven. We are still not sure to what extent dust and lensing are affecting the data, let alone which objects may be directly associated with others. People like Arp have tried to imagine luminary bridges and the like to manufacture speculation in favor of their particular beliefs but no conclusive evidence has yet been produced to come anywhere near warranting any "paradigm shifts" or "novel physics".

In other words, any concerns you may have about discordant redshifts are premature, at best.

George
2007-Jul-04, 07:44 PM
BAUT member Bill Keel has studied many cases (http://www.astr.ua.edu/keel/research/dust.html) with similarities to your hypotheticals. Perhaps a good way to address the general question which your more restrictive OP is a part of would be to ask why the galaxies in Keel's studies have 'discordant' redshifts? Yes, a very good suggestion. If indeed you do have "proof" to the contrary, folkhemmet, please offer it.

[It is no coincidence that Bill's avatar is of NGC3314 (http://nrumiano.free.fr/Images_gx2/NGC3314.jpg). The larger galaxy is in the background about 25 million lyrs behind the smaller one in the foreground. Apparent sizes are only apparent, apparently. :)]

Ari Jokimaki
2007-Jul-05, 04:22 AM
People like Arp have tried to imagine luminary bridges and the like to manufacture speculation in favor of their particular beliefs...

Please show examples of People like Arp imagining luminary bridges.

Please show examples of People like Arp imagining "the like".

Please offer proof that they have done that imagining to "manufacture speculation in favor of their particular beliefs".

jamini
2007-Jul-05, 09:50 AM
Please show examples of People like Arp imagining luminary bridges. Please show examples of People like Arp imagining "the like”.
Oh, you know, the usual pseudoscience proponents and woo woo sites, such as the ones in your own signature. Basically, people who use little more than obscure Rorschach-like imagery to build a false dichotomy argument in support of their own ATM concepts.

Here’s a few more:

Creationist Site (http://www.biblebc.com/CreationEvolution/galaxy.htm)

Tired Light Advocates ( http://ourworld.compuserve.com/homepages/dp5/bol.htm)

Plasma Cosmology Proponents ( http://angryastronomer.blogspot.com/2006/07/big-bang-common-misconceptions.html)

Electric Universe Proponents (http://www.kurzweilai.net/mindx/frame.html?main=/mindx/show_thread.php?rootID%3D54761)



Please offer proof that they have done that imagining to "manufacture speculation in favor of their particular beliefs".
See above. And please refrain from using this as an opportunity to hijack the topic and turn it into a Arp discussion, which has already been debated on this board many times and closed pending any new development. If you have any new evidence to warrant opening a new Arp topic, I will be more than happy to help debunk anything you bring to the table because we simply do not have the technology to come anywhere near justifying any of the claims made by such advocates.

But since the topic of this discussion is: “Discordant redshift question”, and specifically: ”can [it] be definitely proved that galaxies in the same group have vastly different redshifts”. What direct proof can you present to demonstrate conclusively to exactly what extent and precisely where any alleged discordant redshifts are taking place?

Please note that this is a direct request for specific conclusive data. I am not soliciting your opinions or asking for your personal interpretations of what amount to Rorschach Tests.

Ari Jokimaki
2007-Jul-05, 11:18 AM
Oh, you know, the usual pseudoscience proponents and woo woo sites,...
"People like Arp" publish in peer-reviewed journals, so it's kind of hard to see how that answers my query. And I was asking specific examples, not some obscure website links. If your example is NGC 4319 which seems to be the topic of your first reference, then the bridge is there, it's only a question if it's a real or just apparent bridge, result of chance projection.


And please refrain from using this as an opportunity to hijack the topic and turn it into a Arp discussion,...
I was just asking you to back up your claim, or rather to show that there was anything else in you comment than baseless badmouthing. Please refrain from playing a moderator.


What direct proof can you present to demonstrate conclusively to exactly what extent and precisely where any alleged discordant redshifts are taking place?
I haven't made any claims here, so I'm not going to present anything in this thread, remember also that this is Q&A forum, so I can't talk ATM here. (Nor am I interested in debating that again, it just ends up having to deal with nothing but those nonsense badmouthing "arguments" without any scientific content like yours.)

jamini
2007-Jul-05, 11:22 AM
I haven't made any claims here, so I'm not going to present anything in this thread, remember also that this is Q&A forum, so I can't talk ATM here. (Nor am I interested in debating that again, it just ends up having to deal with nothing but those nonsense badmouthing "arguments" without any scientific content like yours.)
Well then, I suppose that concludes your participation in this topic. Thanks for the discussion.

folkhemmet
2007-Jul-05, 11:43 AM
The topic of discordant redshifts is actually very new to me so I appreciate all of the perspectives and answers to my questions that this thread has received. Tim's point about peculiar velocities, for example, is something that I wondered might be playing some role in the topic of discordant redshifts, but his post provided a well-written clarification of that issue. I also get what some people have been saying about the term discordant redshift itself-- it is easy to get the feeling that it assumes what it sets out to prove.

Cougar said: "Actually, no, I don't think so. There are too many observations confirming the redshift-distance relation. If, as you say, "it can be definitely proved that galaxies in the same group have vastly different redshifts," then rather than throwing out the whole idea of the expansion of the universe, I would think a solution more local to the anomalous phenomenon would be sought." This is exactly what I've been thinking. It's been said over and over again that all it takes is one piece of disconfirming evidence to overturn a paradigm. However, one should also have to see how well the contrary view which in the case of discordant redshifts is that the Universe is not expanding and compare it with other evidence and see how if it coheres with that other evidence. In other words, lots of powerful evidence indicate that the Universe really is expanding and so discordant redshifts are probably due to some other combination of phenomena which are less dramatic in nature than a paradigm shift.

Right now I am on a quest of sorts to find out if the standard model of cosmology is likely to be correct in the sense that it will, at least in its most basic form, be taught a thousand years from now. Of course it is always possible to doubt and be skeptical, and some people are still skeptical of the obseved fact that the Earth is round and revolves around the Sun, so I am looking for reasonable challenges to the dominant Big Bang paradigm. And I know there is proabably no theory-independent way of telling what is "really there" in nature, but this type of doubt pervades all aspects of life and is not limited to scientific investigations. The point, and I get the feeling Nereid agrees, is that one cannot logically have it both ways-- play the radical skeptic card when dealing with others' views and then use the scientific method to buttress their own view.

Nereid
2007-Jul-05, 01:40 PM
Perhaps it's worthwhile to look a little more closely at the 'discordant' part of 'discordant redshifts'.

First though, 'redshifts': AFAIK, the 'redshift'1 for an astronomical object (source of photons from the sky) is measured, directly2, in only one way: 'lines' observed in spectra are assigned to certain atomic3 transitions, and the difference between the 'lab' frequencies (or wavelengths) and the observed frequencies becomes a redshift.

'Discordant', when applied to redshift, requires several interpretations, or assumptions, and some logic.

For example, 'discordant redshifts' only exist where there is a comparison between the redshifts of two (or more) objects; a single object, itself, cannot have a 'discordant redshift'.

Perhaps the most common assumption, or interpretation, associated with 'discordant redshifts' is that of similar distance - the two (or more) objects are assumed to be at a similar distance from us. Or independent methods are used to estimate the distances to the two objects (either absolute or relative), and when the two distance estimates are sufficiently close, comparison of their redshifts can be made to see if they are 'discordant'.

While there is, sometimes, some uncertainty about the (directly observed) redshift of an astronomical object, by far the trickier part of establishing a case of 'discordant redshift' concerns the assumptions, or interpretations, on distances.

Unfortunately, for individual extragalactic objects, distances are quite difficult to estimate with a precision that is even 10 times worse than that with which the redshift can be (directly) determined.

- - - - - - - - - - - - Let me return to the redshifts themselves - - - - - - - - - - - - -

There's a truly astonishing thing about redshifts: they only make sense if you assume the photons you detect4 were emitted by atoms that behave exactly the same way that atoms behave in our Earthly labs!

And it gets even more astonishing: quite a few of the lines observed, and used to determine redshift, have not, in fact, been observed in any Earthly lab - several are 'forbidden lines'.

In other words, 'redshift', as an observed characteristic of an astronomical object, depends completely upon assumptions to do with the reality of atoms behaving exactly as predicted by modern quantum theory.

There's an interesting corollary to this: it's just past the US Independence Day holiday, and I imagine many folk reading this watched spectacular fireworks displays in the evening - reds (produced by strontium and/or lithium compounds), yellows (sodium), greens (barium), and blues (copper).

Suppose, somehow, strontium, sodium, barium, and copper compounds could be brought to Earth, from a planet in a galaxy with a highly discordant redshift (in the sense of being much higher than the others at its estimated distance), should such an astronomical object be found. Suppose these were made into fireworks, for use on a US Independence Day evening.

What colours would you see from these 'discordant redshift' fireworks?

1Which may be negative, so is a blueshift.
2'Redshift' can also be estimated, indirectly, from 'synthetic spectra' and from the broadband SED (a.k.a. 'colours').
3Sometimes molecular or nuclear.
4Or don't detect, in the case of absorption lines.

Cougar
2007-Jul-05, 01:56 PM
And it gets even more astonishing: quite a few of the lines observed, and used to determine redshift, have not, in fact, been observed in any Earthly lab - several are 'forbidden lines'.
Well, yes, they're called "forbidden" lines, but actually they just relate to atomic transitions that are very unlikely, but obviously not impossible. As Wiki (http://en.wikipedia.org/wiki/Forbidden_line) notes....


Forbidden emission lines have only been observed in extremely low-density gases and plasmas, either in outer space or in the extreme upper atmosphere of the Earth. Even the hardest laboratory vacuum on Earth is still too dense for forbidden line emission to occur before atoms are collisionally de-excited.

ngc3314
2007-Jul-05, 01:57 PM
A couple of points on discordant redshifts in galaxy groups -

There has been much analysis of the compact groups catalogued by Paul Hickson, of which Stephan's Quintet is one and not too atypical. A sizeable minority of these have one member whose redshift differs from the mean of the rest by more than, say, c*delta z=3000 km/s. These outliers fit into the overall redshift structure in their part of the sky. As a couple of students found while working with Jack Sulentic (although I can't find at the moment whether they ever published this), in almost all these cases, the outlier shared its redshift with large-scale structures that show up in redshift-angle plots (as seen in the famous "slice of the Universe" diagram or the Sloan plot here (http://www.sdss.org/news/releases/galaxies.jpg)). This suggests that, as a sample, the redshifts of these galaxies don't have anything to do with the group location.

Overlapping galaxies (a specialty of the house) furnish a bit more data on the question, since in these cases it is unambiguous what is in front and what's behind. Redshift differences in these show plenty (well, of a sample of perhaps 20) with wrong-way differences up to about 600 km/s (i.e. the higher redshift in front), and one single case beyond that. This record-holder is the foreground gas-rich system in front of NGC 1275 at the center of the Perseus galaxy cluster, and has a redshift 3000 km/s greater than NGC 1275 itself. That's at about the 95th percentile of velocities one would expect from the random motions in the cluster. Finding a pair the "wrong way around" with a difference of, say 5000-10,000 km/s and not even in a rich cluster would be a very interesting thing. (In many of these cases, absorption lines from interstellar gas can confirm the front-back assignments from dust absorption if there is enough observing time available).

peteshimmon
2007-Jul-05, 05:40 PM
Obvious question to ask if I may...are there
any super Hubble spacecraft images of these
objects or "bridges" that may..ahem..shed
light on the subject?

Tim Thompson
2007-Jul-05, 05:43 PM
It's been said over and over again that all it takes is one piece of disconfirming evidence to overturn a paradigm.
Well, one piece of disconfirming evidence can falsify a theory, or overturn a paradigm. An ATMer will often insist that any one piece of disconfirming evidence will do the job, but that's not the case. The one piece trick only works when that one piece creates an intolerable conflict between the theory and the observation. In my estimation, the question of discordant redshifts has never achieved that status, even if we grant that there are as many truly "discordant" objects as has been alleged. My reason for thinking this way is as Cougar said, there is simply way too much evidence confirming a real redshift distance relationship for galaxies & quasars. It makes far more sense to look for specific causes for the appearance of "discordance" in a group, than to simply ignore a well established redshift distance relationship. Keep looking for specific exceptions, until something finally causes an intolerable conflict.


Right now I am on a quest of sorts to find out if the standard model of cosmology is likely to be correct in the sense that it will, at least in its most basic form, be taught a thousand years from now.
I think that the most basic idea, that of an expanding universe, is in fact that "correct". But remember, scientific theories are never "right" or "wrong". Rather, scientific theories are either "consistent" or "inconsistent", as compared to observations. It is common enough to call a theory "correct" when it has established a long track record of consistency. We just need to remember what the words really mean.

Of course, we should also keep in mind that 1000 years is a long time. Nevertheless, Newtonian physics, already about 400 years old, is well set up as the master paradigm of basic physics for 1000 years. I think the idea of expansion is of similar strength, although the details by which it works are still up for grabs (i.e., the idea that the expansion is accelerating is only about 10 years old).


... so I am looking for reasonable challenges to the dominant Big Bang paradigm.
In My opinion, the only reasonable challenges to the dominant big bang cosmology come from Jayant Narlikar, who was a student of Fred Hoyle. With that in mind, I might suggest a few examples worth reading; i.e., Standard Cosmology and Alternatives: A Critical Appraisal (http://adsabs.harvard.edu/abs/2001ARA%26A..39..211N) (Annual Review of Astronomy and Astrophysics, 2001) & Action at a Distance and Cosmology: A Historical Perspective (http://adsabs.harvard.edu/abs/2003ARA%26A..41..169N) (Annual Review of Astronomy and Astrophysics, 2003). Neither of these are available online, except the abstracts, ARAA never allows free access tp preprints or offprints. But if you can find the Annual Review series in a library, these are as good as anti big bang science gets, and are fairly comprehensive reviews, though a bit dated perhaps. Some of his more recent works are available online, though not particularly geared for the general reader; i.e., nterpretations of the Accelerating Universe (http://adsabs.harvard.edu/abs/2002PASP..114.1092N), Narlikar, Vishwakarma & Burbidge, PASP 114(800): 1092-1096, Oct 2002; Inhomogeneities in the Microwave Background Radiation Interpreted within the Framework of the Quasi-Steady State Cosmology (http://adsabs.harvard.edu/abs/2003ApJ...585....1N), Narlikar, et al., ApJ 585(1): 1-11, March 2003; QSSC Re-Examined for the Newly Discovered SNe Ia (http://adsabs.harvard.edu/abs/2005IJMPD..14..345V), Vishwakarma & Narlikar, IJMP-D 14(2): 345-354, 2005; On searches for gravitational waves from mini-creation events by laser interferometric detectors (http://adsabs.harvard.edu/abs/2006MNRAS.369...89S), Sarmah, Banerjee, Dhurandhar & Narlikar, MNRAS 369(1): 89-96, June 2006. "QSSC" is Quasi Steady State Cosmology (http://www.iisc.ernet.in/pramana/dec1999/c3.html), developed originally by Fred Hoyle out of the old steady state cosmology (http://en.wikipedia.org/wiki/Steady_state_theory) of the 1950's (but also see Ned Wright's Errors in the Steady State and Quasi-SS Models (http://www.astro.ucla.edu/~wright/stdystat.htm)).

There are also books, i.e. Current Issues in Cosmology (http://www.amazon.com/Current-Issues-Cosmology-Jean-Claude-Pecker/dp/0521858984/ref=sr_1_4/104-1089100-8419967?ie=UTF8&s=books&qid=1183655724&sr=1-4), Pecker & Narlikar, Cambridge University Press, 2006; An Introduction to Cosmology (http://www.amazon.com/Introduction-Cosmology-J-V-Narlikar/dp/0521793769/ref=sr_1_4/104-1089100-8419967?ie=UTF8&s=books&qid=1183656086&sr=1-4), Jayant Narlikar, Cambridge University Press, 2000. The latter is a formal text book in cosmology not suited for the general reader. But there is a chapter on alternative cosmologies, which might be informative. And, finally, it helps to understand the standard model if you want to appraise the alternatives. With that in mind, I suggest Cosmology: The Science of the Universe (http://www.amazon.com/Cosmology-Science-Universe-Edward-Harrison/dp/052166148X/ref=sr_1_1/104-1089100-8419967?ie=UTF8&s=books&qid=1183656434&sr=1-1), by Edward Harrison, Cambridge University Press 2000 (2nd ed). This last book is very readable, by anyone, and perhaps the best book you will find on general cosmology (in my opinion).

Online, see Ned Wright's extensive Cosmology Tutorial (http://www.astro.ucla.edu/~wright/cosmolog.htm), the best online resource for cosmology.

ngc3314
2007-Jul-05, 06:45 PM
Obvious question to ask if I may...are there
any super Hubble spacecraft images of these
objects or "bridges" that may..ahem..shed
light on the subject?

There are HST images of NGC 4319/Markarian 205, the best case Arp has presented for a bridge between objects at substantially different redshifts. They were released (http://heritage.stsci.edu/2002/23/index.html) by the Hubble Heritage team. The team was so sensitive to possible accusations of doctoring that they didn't even apply the usual and standard cosmic-ray rejection to the region in question. Sadly, the structure doesn't have any high-surface-brightness structure that benefits from HST's resolution; we didn't learn much that wasn't already seen in ground-based images. I once did the exercise of subtracting models for the outer regions of both NGC 4319 and Mkn 205, based on the other parts of their images; one can confirm that there is a smooth feature between them, in excess of the starlight halos of both. The feature is faint enough that I probably wouldn't have noticed it on these data had I not been looking specifically; Hubble is not the tool of choice for large, low-surface-brightness objects. While elongated, this feature is radial to neither NGC 4319 nor Mkn 205. It does arc smoothly into the small companion galaxy to Mkn 205 (which is the main reason I concur with a paper by Stockton and MacKenty based on Mauna Kea image, that it is most likely a tidal tail from an interaction between Mkn 205 and a small companion galaxy). NGC 4319 does look disturbed, but it also has a similarly bright companion galaxy (NGC 4291) which is sometimes cropped out of published images. (In checking that ID, I just learned that wikisky has added a nice new feature linking to images and literature references. Now if I can just remember what I clicked to get it...)

Amber Robot
2007-Jul-05, 06:55 PM
There are HST images of NGC 4319/Markarian 205, the best case Arp has presented for a bridge between objects at substantially different redshifts. They were released (http://heritage.stsci.edu/2002/23/index.html) by the Hubble Heritage team. The team was so sensitive to possible accusations of doctoring that they didn't even apply the usual and standard cosmic-ray rejection to the region in question.

The photo you link to has clearly been cosmic-ray cleaned, etc. Is there a version you can link to that hasn't?

ngc3314
2007-Jul-05, 07:20 PM
The photo you link to has clearly been cosmic-ray cleaned, etc. Is there a version you can link to that hasn't?


Most of it has anyway - one of the team members once mentioned that they hadn't auto-cleaned the area right around the bridge (I should clarify, now that I think of it, that this referred to the frequent use of judgment and interactive procedures to clean the remaining cosmetics that sneak past the automated routines). There is a link there (top right) to "original images". As a sample, I'm posting a section of the I-band imaging from the PC CCD, which combines two original exposures using the standard "crreject" processing to ignore pixels which are higher above the average than statistics and the detector noise would suggest (i.e. pixels that were so high in only one exposure that they must be contaminated by cosmic-ray events).

Note to bystanders: one can always start at the HST archive (http://archive.stsci.edu/hst/search.php) and get data lists and GIF previews. For any software but IRAF/STSDAS and IDL, the peculiar implementation of FITS storage for the four WFPC2 CCDs is a problem (and is always really annoying), but FITS viewers are available for lots of platforms (DS9 has a Windows version, for example). Looking at the preview for some of the individual NGC 4319 exposures shows how pimply with CR events any long-exposure HST image becomes (and that search lets you inspect all of them - the Heritage images have names starting with U6LU01). I just attached the half-size GIF preview for one of the single 10-minute B-band exposures (the full-size image was a bit too large for the forum's size limits).

Amber Robot
2007-Jul-05, 07:29 PM
Which image is which there? The right image is of the entire WFPC2 field of view, not just the PC chip.

I don't see a "bridge" in either of these photos. At least nothing obvious.

Nereid
2007-Jul-05, 07:41 PM
This MAST page (http://archive.stsci.edu/xcorr.php?target=NGC+4319&max_records=10&action=Search&resolver=SIMBAD&missions[]=WFPC1&missions[]=WFPC2&missions[]=WFPC2_ASN&missions[]=FOC&missions[]=ACS&missions[]=UIT&missions[]=STIS&missions[]=GALEX&missions[]=XMM-OM&missions[]=NICMOS) may be of some help (re NGC 4319) ...

jamini
2007-Jul-05, 07:43 PM
I don't see a "bridge" in either of these photos. At least nothing obvious.

Don't worry; neither did the rest of the astrophysics community. ;)

ngc3314
2007-Jul-05, 07:46 PM
Which image is which there? The right image is of the entire WFPC2 field of view, not just the PC chip.

I don't see a "bridge" in either of these photos. At least nothing obvious.

The first (left) is part of the PC chip after CR rejection. The right image is the full field (4 chips) from a single exposure, CRs and all. The bridge really doesn't show up until you smooth the frames and stretch a lot more than the automatic preview does. Ahh, here we go - here's a false-color version of the V image with smoothing (I think it was 3x3 pixels, maybe even with a median filter to improve cosmetics), from a 4-chip mosaic but showing mostly part of the PC frame. The feature is there but pretty underwhelming without the smoothing and stretching. Part of the outer regions of NGC 4319, incompletely subtracted from imperfect modelling using elliptical symmetry, shows up to the lower right. The feature in question extends outward from the lower right part of the image of Mkn 205, toward 5 o'clock in this display. Looking back at smoothed images without model subtraction, the other feature pointing toward the edge around 2 o'clock is an artifact of the NGC 4319 galaxy model getting poor at that radius.

Ari Jokimaki
2007-Jul-06, 05:25 AM
Well then, I suppose that concludes your participation in this topic. Thanks for the discussion.
You make a claim, I ask you for details about it, then you suddenly demand me to prove something to you, and when I don't do that you try to kick me out of the discussion? You really have a hard time backing up your claim, don't you? I'm not surprised though, many times when there is a discussion about discordant redshift question, there are some people who just parrot the "Arp is just a crank" type of arguments. When you try to ask them details of their "arguments", the evasive maneuvres start, like we have seen here.



I don't see a "bridge" in either of these photos. At least nothing obvious.
Don't worry; neither did the rest of the astrophysics community.
ngc3314, part of astrophysics community, seems to see the bridge for example. And here's a page from Hubble heritage website (http://heritage.stsci.edu/2002/23/supplemental.html) where someone also sees the bridge.

That bridge is not difficult to bring out from HST images, I have attached an image from Hubble heritage website (http://heritage.stsci.edu/2002/23/original.html) which I have processed in image processing software. Used image is the one with the text " This composite image of B, V, and I datasets has been log streched to enhance the faint features in the image" below it. I have adjusted contrast to the max, and then reduced brightness so much that noise in the image is not visible. There are still faint features left in the image between NGC 4319 and MRK 205. Note that you can't create not existing features to the image with contrast and brightness adjustment, so what I really did was just to enhance the real features in the image, and anyone with image processing software can repeat what I did.

There was for a long time a debate whether the bridge exists there or not, but as far as I know, currently the astrophysics community has accepted that the bridge is there, it is just not accepted that it is a real connection between the two objects. Instead, like ngc3314 says, it is generally thought to be a chance projected background feature, possibly a tidal tail. Here is a paper by Cecil & Stockton (1985) (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1985ApJ...288..201C&db_key=AST&data_type=HTML&format=&high=438d9feb8a25896) making a case for that kind of thing. Notice that the Authors are part of astrophysical community and even the title of their paper mentions "luminous feature between Markarian 205 and NGC 4319".

So, I suggest that before you make further arguments, please get familiar with the subject first. You'll find it much easier to argue against the subject after that, and you will then make much more convincing arguments.

jamini
2007-Jul-06, 12:56 PM
part of astrophysics community, seems to see the bridge for example. And here's a page from Hubble heritage website (http://heritage.stsci.edu/2002/23/supplemental.html) where someone also sees the bridge.
From your own source (http://heritage.stsci.edu/2002/23/supplemental.html):


Enhanced stretches of the HST image show a debatable "luminous bridge" between NGC 4319 and Mrk205


However, the question is whether this nebulosity implies that there is a real, physical connection between the two galaxies, or whether it is just a little bit of irregularity in the structure of NGC 4319 or Mrk 205, that happens to lie between the images. Notice that there are similar nebulous features on the edges of both objects in other places as well, not just between them. I don't think that these images demonstrate that there is a real connection between the objects, but you can make up your own mind.[emphasis added]


In the view of most astronomers, the juxtapositions are just due to chance. The filamentary connection became less convincing as better images became available. John Bahcall and collaborators made a noteworthy contribution when they showed that NGC 4319 absorbs some of the light from Mrk 205, just as expected if NGC 4319 is projected in front of Mrk 205 (Astrophysical Journal 1992). In time, many quasars were found to lie in galaxies with exactly the same redshift, providing powerful evidence that quasars are an event that occurs in the nucleus of galaxies.
Today the redshift controversy has almost faded from view. Only a few astronomers still think there is reasonable evidence for noncosmological redshifts; a recent summary making their case was published by Geoffrey Burbidge (Publications of the Astronomical Society of the Pacific 2001). The vast majority of astronomers think that the evidence is overwhelming that redshifts show distances to objects in the expanding universe.[emphasis added]

Got anything else?

Or better yet, since the topic of this discussion is: “Discordant redshift question”, and specifically: ”can [it] be definitely proved that galaxies in the same group have vastly different redshifts”. What direct proof can you present to demonstrate conclusively to exactly what extent and precisely where any alleged discordant redshifts are taking place?

Please note that this is a direct request for specific conclusive data. I am not soliciting your opinions or asking for your personal interpretations of what amount to Rorschach Tests.

Ari Jokimaki
2007-Jul-06, 02:17 PM
From your own source (http://heritage.stsci.edu/2002/23/supplemental.html):

Got anything else?
I never claimed it was a real bridge, and I will not claim it is a real bridge. I pretty much agree on the things said in the Hubble heritage page I linked to. Point is that there is some material between the galaxies, which can be interpreted as a bridge, so nobody has been imagining or making up any evidence in that case. The apparent luminous bridge is there.

I'm still not seeing much evidence to your "imagining bridges and the like", and definitely not for "manufacturing speculation etc.". If you would have it, you would have given it already.


What direct proof can you present...
You still don't get it, do you? :wall: I'm here only asking you to present specific evidence to your claim (which clearly is not coming). I'm not here to present a case for discordant redshifts, I don't have any need for that. So stop trying to shift the burden of proof on me.

jamini
2007-Jul-06, 02:45 PM
I never claimed it was a real bridge
Good, neither does anyone else in mainstream astronomy.

"Not real" and imaginary are synonymous.



I'm not here to present a case for discordant redshifts
Well then, I guess we agree on that too.

George
2007-Jul-06, 03:36 PM
"Not real" and imaginary are synonymous. Ari said it nicely in his original post...


If your example is NGC 4319 which seems to be the topic of your first reference, then the bridge is there, it's only a question if it's a real or just apparent bridge, result of chance projection. There is something apparently there, that is all that is apparently known.

Nereid
2007-Jul-06, 03:59 PM
Whatever the data contains, to what extent does calling it a 'bridge' bias a reader to (or away from) a particular interpretation, no matter how you might wish (or intend) no such bias?

If instead you make up a new term - trewas, say - for 'extended low surface brightness features with {insert succinct description of shape here}', and say that there is a {insert values of trewas parameters here} trewas located {insert position data here}, to what extent does that remove any intended or unintended implication (or conclusion!)?

One potential advantage of defining something like a trewas is the opportunity to study their distribution, in many wavebands, just about all over the sky, in a pretty objective way ... with a sufficiently careful definition, and good coding, you could develop an automated search capability, and let it loose on as many FITS images as you could find.

For any serious attempt to determine the characteristics of 'galaxy-galaxy trewases' or 'galaxy-quasar trewases', I think you really have little choice but to adopt such an approach. After all, the number of resolved galaxies for which there are well calibrated FITS images is now in the millions (and if you add different wavebands, tens of millions of images), and for quasars (or QSOs, depending on your definition), at least a hundred thousand. Even the best trained human brain, as pattern detector, is quite unreliable when it comes to objectively finding patterns in such large datasets.

dgruss23
2007-Jul-10, 12:33 PM
Many baut forum viewers/members are probably aware of the debate over the implications of discordant redshifts. First of all, certain groups of a galaxies may have a member galaxy with a vastly different redshift than its neighbors. If it can be definitely proved that galaxies in the same group have vastly different redshifts, then the entire paradigm of an expanding Universe in which redshift and distance are intimately related would be called into serious question.

In some cases a galaxy with a discordant redshift may be smaller than the other galaxies and may just appear to be close to the lower redshift galaxy when in actuality it is a larger galaxy much further away. However, what about cases in which the galaxies are of very similar angular sizes and part of the same group AND they have discordant redshifts? Are there simpler more mundane explanations that don't involve novel physics that could explain a situation like this?

folkhemmet,

We had a lot of discussions on this topic in the Arp et al thread in ATM.

Here (http://www.bautforum.com/against-mainstream/26365-more-arp-et-al-28.html#post716014)is the page (if I linked this correctly) in which the bridges discussion started.

Here (http://www.bautforum.com/716014-post1119.html)and here (http://www.bautforum.com/716015-post1120.html)are the two long posts in which I started off the bridges discussion. You might find it interesting to read the discussion that followed those posts.

There is a tremendous amount of reading involved in that thread. With the 30 day rule the thread can no longer be posted to so you cannot ask questions there. Nor can we get into discussion here in Q&A because that would involve advocacy of discordant redshifts (an ATM idea). But if you have any additional questions just send me a PM.

antoniseb
2007-Jul-10, 12:41 PM
With the 30 day rule the thread can no longer be posted to so you cannot ask questions there. Nor can we get into discussion here in Q&A because that would involve advocacy of discordant redshifts (an ATM idea).

If either of you have new data (not previously discussed), we can start a narrowly focused 30-day thread in ATM.

dgruss23
2007-Jul-10, 10:14 PM
If either of you have new data (not previously discussed), we can start a narrowly focused 30-day thread in ATM.

There is new data, but I was trying to point folkhemmet to some earlier discussion relevant to the OP. Although if he/she should have questions on the content of that earlier discussion I really don't know with the rules as they are how folkhemmet is to get answers unless via PM.

peteshimmon
2007-Jul-11, 05:59 PM
I must thank ngc 3314 for posting those
images in responce to my query. I am of an
age where it still amazes that one can do
this these days. It is interesting to know
that the investigators were nervous putting
out the pictures. Think I can understand
why now.