Order of Kilopi
That is a point made by Arp in the 1980's. If these high redshift companion are just chance projections, then where are the near misses? Statistically there should be many more of the near misses than examples where the projection occurs right at the end of a tidal tail.Originally Posted by Ari Jokimaki
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Thanks, Ari. I think a few of my examples have tails ending in empty space: the Mice, the Antennae, ARP188.
I have no idea what it proves either, except for the fact that it shows that interacting galaxies do not automatically have a different redshift (I don't think anybody claimed that). So while the mainstream defenders have to see how apparently joined galaxies with different redshifts can be explained (by e.g. showing that they are not joined, but doing this obviously by something else than redshift alone), Arpians perhaps have to explain when / how / why some (most?) interacting galaxies have the same redshift, and others don't. But this may fall outside of the current scope of this discussion.
Personally, while I don't for the moment see a problem (for the mainstream explanation of redshifts) with e.g. Stefan's Quintet, I haven't seen a good mainstream explanation for NGC7603 yet.
While confirmation (if possible) that the two anomalous redshift objects in it are really linked to the bridge would mean a serious blow to the view that redshift equals distance (I'm oversimplifying), I don't think it would mean that that system is wrong, as there are too many "close" examples where cepheids or other systems correspond to the redshift. The redshift rule would have to be adjusted and applied much more cautiously, but not abandoned.
I just thought it would be good if I gave my own view of this, I'm not representing anyone's position (either side) here...
Order of Kilopi
Thanks for sharing that Fram! And I agree with the last part of your statement as well. There certainly is a Hubble relationship. It would be foolishness to suggest that redshift does not increase as objects get more distant. All Arp et al are suggesting is that in addition to this increase in redshift with distance some objects - such as the objects apparently in the bridge of NGC 7603 - may exist which have an additional redshifting component that would require a new explanation. I don't think a correct mechanism for this additional redshift has been found - but that remains a separate issue from empirically establishing that it might exist.
And thanks too for you work at listing examples where the differences are small.
Order of Kilopi
What? I never made such a statement.
For the record, I feel this is a lot like requiring a boxer to fight with one hand tied behind his back.
Everyone is entitled to his own opinion, but not his own facts.
Order of Kilopi
Nereid,
I took a look at your links. Most of them are BAAS articles which are just abstracts. If you could find more detailed articles that you believe are relevant to this discussion and explain how you see them as relevant I would be glad to look at them.
Order of Kilopi
I believe the evidence forces us to conclude the former, and I am flabbergasted that you continue to oppose reaching that conclusion.
But if you recall, you had claimed that bridges were evidence of interaction, and I said sometimes yes, sometimes no; and you asked When are they not? And NGC 7320 was just an example showing that while bridges often show interaction, this is not always the case, and therefore the existence of a bridge between two objects does not conclusively show they are interacting. Ari, bless his heart, has just provided additional examples.
Hmm. Obviously I don't remember that discussion.
Everyone is entitled to his own opinion, but not his own facts.
Order of Kilopi
Its not at all. We're looking at two different interpretations of redshift. You cannot use one interpretation to disprove another interpretation. You must use observational evidence. I find it remarkable that - when faced with examples like NGC 7603 and NEQ3 that we're providing observational evidence that the objects in question are interacting and the only response is that they cannot be because the redshifts are different.
I've directly asked this yesterday- what are the tests that show that these objects are not interacting? That is the mainstream view. Surely there is compelling evidence to back up all this certainty.
Order of Kilopi
Wait - what is the bridge in NGC 7320? And what specifically has Ari provided that are examples that the bridges are not evidence of interaction.
Established Member
Here is a wonderful shot of M51 - the hi-res version is my wallpaper.
http://www.astro.princeton.edu/~rhl/PrettyPictures/
Seeing the way the spiral arm ending on 5195 is distorted and thinned, and observing the shredded appearance of the inner arm, it is difficult to call this anything but an interacting pair. In fact, it looks like the companion was ejected from the host through the plane of the disk.
Last edited by turbo-1; 2006-Apr-06 at 03:54 PM.
Order of Kilopi
Oops - I simply started at the bottom of Bill's publication page (the one I provided a link to in my post #1194), but didn't check (they are, as you note, meeting abstracts).
If you start at the top of the page, and select likely looking papers by their titles ... (you have >100 to choose from).
For example, there are four papers with the title "Seeing Galaxies Through Thick and Thin {n}"
Some others that might be helpful:
91. Deep HST Galaxy and Pair Counts as Constraints on Merging History, Wentao Wu and William C. Keel, AJ 116, 1513 (1998). ( ADS | e-AJ)
88. Gravitational Interactions and Ram-Pressure Stripping in Poor Groups, David S. Davis, William C. Keel, John S. Mulchaey, and Patricia A. Henning AJ 114, 613 (1997). ( ADS)
83. Rotation Curves and Velocity Measures for Spiral Galaxies in Pairs, Astrophys. J. Supplement 106, 27 (1996). ( ADS)
73. Mass Transfer and Star Formation in the Early-Type Galaxy of a Mixed Pair, AM 0327-285, D.F. de Mello, W.C. Keel, J.W. Sulentic, R. Rampazzo, E. Bica, & R.E. White III, Astron. Astrophys. 297, 331 (1995). ( ADS)
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If we are to test the assumption that redshift is the sole indicator of distance, we have to use all the observational tools at our disposal. Again, nobody here is saying that the Hubble relationship does not exist. We are exploring the possibility that objects can have intrinsic redshift over and above that resulting from their cosmological distance from us. To do this, we have to study the evidence for interaction to see if we can establish with some degree of confidence whether objects are interacting or not independent of their redshift measurements.
Do you have something specifically related to the subthread about bridges as evidence for interaction? dgruss23 has done a lot of work preparing for this discussion, and it would be a shame not to take advantage of that.
Order of Kilopi
Perhaps I read his post too quickly and missed the context of statements such as, "Yet now even the shape of that "bridge" warns of an impostor.... This makes IC 3483 presumably just a foreground galaxy."
Everyone is entitled to his own opinion, but not his own facts.
Established Member
To continue on the subject of bridges, Bill Keel has studied the interacting pair NGC 1409/1410, which are embedded in a common halo of stellar material and are connected by a bridge of dust - both compelling evidence for interaction.
http://www.astr.ua.edu/keel/research/ngc1410.html
Edit: I found the paper he wrote regarding this interacting system, and it contains some useful discussions on interaction.
http://www.journals.uchicago.edu/AJ/...429617359Guest
Galaxy interactions are clearly linked to bursts of star formation and, in more restricted ways, to the triggering of nuclear activity. What physical mechanisms mediate these connections remains unclear, since there are multiple well-motivated and plausible processes. Among these, mass transfer between the galaxies in an interacting system has long been discussed, but evidence for its occurrence has remained largely circumstantial. Such transfer could play a particular role in dumping gas into the inner regions of a galaxy, since the angular momentum barrier, which restricts the inward transport of disk gas, may be greatly reduced if the gas comes from another galaxy with the appropriate encounter geometry.
Last edited by turbo-1; 2006-Apr-06 at 06:11 PM.
Order of Kilopi
Yes, yes, I understand. It's just that spectroscopy is one of the most profound astronomical discoveries and most significant tools for astronomical research. I understand the question here is its universal applicability as to distance/recession velocity, so it cannot be used as its own support. Still, this line of questioning requires that one of our most powerful tools be left on the shelf. It's like asking someone with a Ferrari to instead travel by horse-drawn covered wagon.
Everyone is entitled to his own opinion, but not his own facts.
Order of Kilopi
But if you're traveling over grassy plains instead of the highway the horse-drawn wagon is the better choice.
With regard to the Hubble relation there are three generic positions we can take:
1. All objects follow the Hubble within the limits of real peculiar motions.
2. There is a Hubble relation - but some objects can have large real deviations from the Hubble relation.
3. There is no Hubble relation.
Now position number 3 is obviously wrong.
Position #1 is the mainstream position whereas position #2 is the Arp et al position we're discussing.
The problem you're having is that you want to use position #1 as proof against position #2 - but that just doesn't work. Each position is really a hypothesis and you don't disprove one hypothesis with another.
Position #3 is not wrong because astronomers accept position#1. Position #3 is wrong because independent distance indicators consistently present a Hubble relation.
In order to have support for position #2 there must be examples for which there is evidence of interaction between objects of vastly different redshifts or a distance derived from a redshift independent distance indicator that suggests the object does not follow the Hubble flow.
Taking NGC 7603. We're saying it has the same signs of interaction that are accepted when redshift differences are small. It doesn't address the issue to respond - "But look at all these samples that seem to follow the Hubble the relation." Our response is "Sure they do - but NGC 7603 doesn't."
If you want to disprove the NGC 7603 association, then it requires specific evidence that the NGC 7603 interaction evidence is not what it seems. That is the evidence we're waiting to see in this discussion - because the case has been presented that there is interaction.
Order of Kilopi
Well if you read the Toomre&Toomre paper what was meant is that the "bridge" is a sign of interaction between the two objects - but due to projection effects it is possible that the two objects are not actually on each end of the bridge. One object could be separated from the bridge and yet be projected as if it is still on the bridge. But whether it is actually physically at the end of the bridge or not it is still the cause of the bridge in the Toomre^2 paper.
That is a very different argument from suggesting that the bridge is not even the result of an interaction between the two objects.
Order of Kilopi
I'd like to hear your thoughts as to the relevance of these papers to the bridges discussion. Specifically, I'm wondering in what ways these papers (1) add support to the mainstream position that the NGC 7603 and other Arp et al cases are not actual interacting systems or (2) add support to the Arp et al case that the the systems are interacting or (3) are these papers a non-factor in this discussion.
Order of Kilopi
The problem I have with NGC 7603 is that the smoothly curving bridge from 7603 does not flow directly into the nucleus of 7603B. It seems to connect north of the center of 7603B. I should think this is not what would be expected if 7603B pulled out the bridge from 7603 due to gravitational interaction. Can this poorly lined up connection be explained?
Everyone is entitled to his own opinion, but not his own facts.
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Due to tidal action and rotation, you can expect some degree of offset between a bridge and an ejected object, however I see a very neatly aligned bridge in this case. Can you link to a photo that demonstrates otherwise?
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http://www.journals.uchicago.edu/cgi...791695394Guest
I have taken the time to search for redshift data for the "apparent" associations that the authors rejected because of discordant redshift.
AM 0407-612 ~4100 km/s diff
AM 0550-342 no redshift for companion in NED, despite the fact that is quite luminous and is located on the end of a very distorted spiral arm. M51 type.
AM 1208-273 ~2300 km/s diff
AM 1921-534 no redshift for companion in NED.
AM 2100-381 very strong optical bridge, but rejected because companion had ~1500 km/s excess v.
AM 2302-502 no redshift for companion in NED.
AM 2359-275 thin straight bridge from host to companion w/ perhaps another ejected object embedded in the bridge near the companion. Rejected due to ~11,500 km/s excess v.
I do not wish for this to derail the subthread on bridges, but thought that some here would be interested in just how much observational work still needs to be done on apparently interacting galaxies. The Arp Madore catalog is not as well-documented spectroscopically as one might expect, and those that are not actively taking part in the subthread on bridges might want to poke around in that catalog and compile a list of pro and con examples for interaction.
Established Member
Here is additional evidence to support the conclusion that NGC 7603 and its companion are actually interacting. It is Figure 1 in the following paper - a deep R-band optical image of the system. It clearly shows that the entire system (including 7603B) shares an extended luminous envelope and that the luminosity increases smoothly the closer you look to 7603 and 7603B. If 7603B were a background object (2x more distant than its host) there is no way that it could have this effect on the host's local environment.
http://www.uni-sw.gwdg.de/~bischoff/pub/2300901.pdf
As I noted earlier in post 1243, Bill Keel has done a lot of work on interacting galaxies and he regards this type of shared luminous envelope as good evidence for interaction. I would like to see some of the supporters of concordance cosmology address this evidence and refute it, if possible.
Last edited by turbo-1; 2006-Apr-07 at 12:11 AM.
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One more statistical anomaly for the stew - why are the small companions so often redshifted WRT the host? Shouldn't we expect to see a number of closer dwarf galaxies superimposed over those bridges and jets and appear blueshifted WRT the host?
Last edited by turbo-1; 2006-Apr-07 at 01:00 AM.
Order of Kilopi
And here is additional evidence that they are not actually interacting.
Anomalous redshift companion galaxies - NGC 7603 - Authored by Sharp, N. A. of AA(Kitt Peak National Observatory, Tucson, AZ)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 302, March 1, 1986, p. 245-256.
Abstract
The bright galaxy NGC 7603 has an extended spiral arm which appears to end exactly on a small, high surface brightness companion (referred to here as NGC 7603B). However, the companion has a much larger redshift than that of NGC 7603, placing it conventionally almost twice as far away. Deep plates presented here show that NGC 7603 actually extends for some considerable distance beyond the companion, and that there is evidence for past interactions which can explain the disturbed structure. Narrow-band H-alpha images show no sign of strong disturbances in the feature apparently leading to NGC 7603B, which would be expected if tidal interaction is currently taking place. A velocity dispersion and a magnitude are also provided for the companion, enabling consideration of the Faber-Jackson relation. Regrettably, the two possible locations for NGC 7603B in the luminosity-dispersion diagram, corresponding to the redshift distances for it and for NGC 7603, bracket the current uncertainties in this relation, and no firm conclusion can be reached. However, two tentative tertiary distance estimates for NGC 7603B agree better with its own redshift. Other redshift measurements in the vicinity reveal the presence of a group at the same distance as NGC 7603, but there does not appear to be a cluster at the companion's distance (although there is a yet more distant group). No strong anomalies have been found which would force the acceptance of the existence of a noncosmological redshift.
Everyone is entitled to his own opinion, but not his own facts.
Established Member
You may note that the paper you cited was written in 1986, 14 years before the deep R-band image I linked was available. And this quote is not exactly a ringing endorsement of your view, even at that epoch.
The NGC 7603 system is demonstrably a system and not a chance alignment. It is up to us to determine how this might be explained. If you can come up with an explanation for this, I will gladly debate the merits of that explanation with you. The luminosity of the envelope surrounding the NGC 7603 system is quite compelling evidence of interaction. I wish Bill Keel was here with us to weigh in on the importance of the shared luminous envelope to provide evidence for interaction.No strong anomalies have been found which would force the acceptance of the existence of a noncosmological redshift.
Established Member
Not only was this paper written in 1986 as pointed out by turbo-1, but the deep plates mentioned above were obtained in 1973, even longer before today's improved instrumentation. The paper is also couched in much qualifying language, which does not make for a compelling argument.
As for the claim that NGC 7603 extends for some considerable distance beyond the companion, some clarification is needed. The claimed bridge arcs out of the nucleus, and extends either above or below a spiral arm of the galaxy. The galactic arm, lying either above or below the bridge, does extend a longer distance from the nucleus than the bridge, but they are 2 separate objects. So what is really meant by this statement by the author?
TomT
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Another quick read is:
http://www.astr.ua.edu/keel/galaxies/arp.html
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I'm not sure why you linked this, since it contains only a brief and cursory description of the system and no recent imagery. There is nothing new at this link. Do you have anything supportive of the concordance view (or the Arpian view) to contribute?
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So the situation is known, there are not enough near misses?
Do you happen to remember where Arp made the point?
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Yes, let's see if they apply here.
First let's look at ARP 175 image. There doesn't seem to be a lot of images of ARP 175 available, but here is THE ATLAS AND CATALOGUE OF INTERACTING GALAXIES - B.A. Vorontsov-Velyaminov (1959) (This catalog might be important for the whole bridges & interaction discussion). ARP 175 is VV 43. Galaxies in the image of VV 43 in the atlas are marked with a = IC 3481, b = IC 3481A, and c = IC 3483 (I hope I got these right). From the image you can see that there is single, quite long tail.
Of your examples, the Mice and the Antennae have two tidal tails. I think we should reject them because of that, I think we want similar examples with only one tail, agreed?
ARP 188 seems to be a similar case. That makes the total to one. I looked at first 100 cases in the VV-atlas linked above (I might go through them all later), possible (but not good) additional examples are: VV 10, VV 13, VV 33, and VV 34.
I more or less agree with your other comments.
Established Member
I don't see why two tails should be rejected, but it is a minor point.
I think it is logical though that you won't find many examples of galaxies with tails ending in empty space in a catalogue of interacting galaxies, as the tail connecting the two galaxies is the strongest indication of the interaction in most cases.
Absence of evidence... Perhaps VV did not include examples of galaxies with tail but without second galaxy in the neighbourhood because those were, by definition, not "interacting galaxies". On the other hand, perhaps he didn't include those because there weren't any. I'll try to find some examples of galaxies with tails and without nearby galaxies, but this may be a tough search.
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