Order of Kilopi
And I think it is important - if people want to argue this is a chance superposition - to explain why there is a bridge at all. There is not an interacting companion to have formed it except NGC 7603B.Originally Posted by turbo-1
And another thing we might ask. Why -if these are just superpositions - don't we see instances where the bridge passes over the companion? Why do these "accidents" always happen such that the bridge terminates at the position of the "background" object?
Order of Kilopi
I spent some time checking on another possibility. It doesn't allow us to distinguish which distance is better - as I figured it wouldn't. Taking the SBF distances from Tonry et al (2000) I identified galaxies with morphological type similar to NGC 7603B and with mean surface brightness within the D25 isophote within +/- 0.20 mag arcsec-2 of the value for NGC 7603B.
Using the corrected B-magnitudes and D25 angular diameters in HyperLeda and the distance moduli from Tonry et al one can plot the relationship between absolute magnitude and diameter. The sample size that fit the criteria was only 8 galaxies - but they cover a large range in absolute magnitude and form a tight M(B) vs Diameter (kpc) relation. NGC 7603B falls on this relation at the NGC 7603 Hubble distance - but it also falls on the relation at its own redshift distance. If I expand the range of morphological type the sample is obviously larger, but it doesn't appear to have any significant effect on the relation. So as Sharp (1986) found with the Faber-Jackson relation - this test does not allow us to distinguish which of the distances is better.
The reason is that at the Hubble distance NGC 7603B would have a larger absolute magnitude and thus be expected to have a larger diameter. So as we change the estimated distance to the galaxy - the absolute magnitude and diameter slide together along the relation.
What is needed is another parameter to fix the true absolute magnitude of NGC 7603B - such as a rotational velocity. However, NGC 7603B appears to be essentially face on which makes it a poor candidate for TFR anyway. Probably the best hope for getting a distance is advancement in the capabilities of applying the SBF method.
Order of Kilopi
Ok Ari, I had to go back to Toomre&Toomre and take another look at this. Somehow I got myself all twisted around on this this morning.
Anyway, in the context of this discussion, the apparent bridge betwen IC 3481 and IC 3483 is not an example of an instance in which the connected objects have the same redshift but the bridge is not taken as evidence of interaction. IC 3481 and IC3481A have redshifts of ~ 7100 km s-1 while IC3483 has a redshift of 127 km s-1 in LEDA.
So the challenge remains open - can anybody identify an example in which two galaxies are connected by a bridge, have a small redshift differential, and that bridge is not considered a sign of interaction?
Also, just to be clear Ari, were you saying that in this Arp175(vv43) case we see another instance that makes us ask - where are the near misses? Why do the bridges always seem to end at the higher z object? Or were you making a different point?
Order of Kilopi
You're just quoting Arp's "theory", right? You couldn't actually say this with a straight face, could you? I mean, it's just got such a fairy tale quality to it....Three different reasons:
1. A quasar is ejected from a galaxy, then it stops and turns back and finally becomes a satellite to the parent galaxy. During this journey it has evolved to a "regular" galaxy, and as redshift decreases with age, the redshift of the object has become close to the redshift of the parent galaxy (although it should be a bit higher). So we would expect to have more interacting companion galaxies with similar redshift as the parent, because the time the ejected high redshift object is close enough to parent for interaction is only fraction of the time that the more evolved lower redshift companions spend in the vicinity of the parent.
Everyone is entitled to his own opinion, but not his own facts.
Order of Kilopi
As far as how neatly the main bridge (1) is lined up with 7603B, I've shown in the image below how it does not exactly line up with the nucleus of 7603B -- it's off to the north a bit. Now, granted, it's just slightly off, and I don't consider this as conclusive evidence against interaction, but it is a little chink in the armor of Turbo's imagined iron-clad argument.
Then there are the other three fainter "bridges" (2, 3, 4) emanating from NGC 7603, but there don't appear to be any objects at their termini. Are these phantom ejections?
And you both say that bridge #1 terminates at 7603B, and in this image the darker part of that bridge does appear to stop there, but if you look a little closer, it seems like the arc of that bridge continues on past 7603B up into that vast oval area I've labeled "5". Even the red contour lines register its presence.
I agree this is certainly an anomalous system. Even the anomalies are anomalous.
Everyone is entitled to his own opinion, but not his own facts.
Order of Kilopi
As far as how neatly the main bridge (1) is lined up with 7603B, I've shown in the image below how it does not exactly line up with the nucleus of 7603B -- it's off to the north a bit. Now, granted, it's just slightly off, and I don't consider this as conclusive evidence against interaction, but it is a little chink in the armor of Turbo's imagined iron-clad argument.
Then there are the other three fainter "bridges" (2, 3, 4) emanating from NGC 7603, but there don't appear to be any objects at their termini. Are these phantom ejections?
And you both say that bridge #1 terminates at 7603B, and in this image the darker part of that bridge does appear to stop there, but if you look a little closer, it seems like the arc of that bridge continues on past 7603B up into that vast oval area I've labeled "5". Even the red contour lines register its presence.
I agree this is certainly an anomalous system. Even the anomalies are anomalous.
Cougar - thanks for doing that. Actually your yellow lines helped me recognize something I hadn't noticed before. I've previously recognized those filaments, but its easy to get focused on the NGC 7603B filament and the HII galaxies.
Your filament #4 actually does correspond to something. First, you can trace it back to the overexposed edge inside the disk. It comes out of the nuclear region opposite the filament that goes to NGC 7603B. But take a look at this figure from the LC&G paper. Object #23 is actually along the extended line of filament #4. In the LC&G paper object #23 has a redshift of 0.246.
We've talked about the cases in Arp's model of oppositely ejected objects. Ejections often have counter ejections. Object #23 would be the counter-ejection of the z=0.241 object #2 in the filament we've been discussing.
Exciting stuff! Thanks Cougar - and I mean that. I should've noticed that before myself. It clicked when I saw your yellow lines.
As for filament #'s 2 and 3 - there are objects of interest along those paths too. Filament #2 is very faint.
Established Member
Cougar,As far as how neatly the main bridge (1) is lined up with 7603B, I've shown in the image below how it does not exactly line up with the nucleus of 7603B -- it's off to the north a bit. Now, granted, it's just slightly off, and I don't consider this as conclusive evidence against interaction, but it is a little chink in the armor of Turbo's imagined iron-clad argument.
Then there are the other three fainter "bridges" (2, 3, 4) emanating from NGC 7603, but there don't appear to be any objects at their termini. Are these phantom ejections?
And you both say that bridge #1 terminates at 7603B, and in this image the darker part of that bridge does appear to stop there, but if you look a little closer, it seems like the arc of that bridge continues on past 7603B up into that vast oval area I've labeled "5". Even the red contour lines register its presence.
I agree this is certainly an anomalous system. Even the anomalies are anomalous.
Neat graphics. I need to learn how to do this.
First, a general question to all. NGC 7603 is a Seyfert I, a type of spiral galaxy. Why don't we have a clear image of the spiral arms?
INMHO, in the image to which you have neatly added graphics:
1. The bridge IS centered on NGC 7603B.
2. Line #2 is the south spiral arm of NGC 7603 which extends past the end of the bridge almost to the dark object in the upper left.
3. Line #3 is the base of the north spiral arm which curves downward toward the dark object at the lower right.
4. Line #4 doesn't appear to be anything to me.
5. The "vast oval area " you label as 5 appears to me to be the continuation of the south spiral arm of NGC 7603.
As far as the spiral arms of NGC 7603, I will stand corrected if someone can reference a clear image of NGC 7603 showing it's spiral arms in a different location than I have postulated.
TomT
Established Member
This just shows that sometimes it happens even to the best of us.
No, that's it. Well, I wasn't thinking just near misses, I was thinking also far misses, or misses in general. Like I said before (I don't know how many pages back), if ARP 175 and other similar cases (NEQ3 for example) represent a situation where the tidal tail of two objects happens to end at discordant redshift object, there should be a lot more cases where the tidal tail misses (near or far). So, I wasn't actually thinking about all cases with bridges, only those where there are two objects with similar redshift (producing the tidal tail) and a third discordant redshift object (trying to hit or miss the end of the tidal tail).
Established Member
Yes, or rather the empirical model.
Yes I can. Sure it contains some assumptions, but not more than other cosmologies.
C'mon, we're talking about cosmological theories here, they're all just fairy tales at this point.
Established Member
Ok, so they are created by the interaction. What I'm wondering about NGC 772 is that what has caused the tidal tail? At least I can't see there any obvious candidate for interaction.
Btw. your link didn't work for me. It might be better to give links to the abstract page (here's the abstract page of the paper in question), as I think that the PDFs don't stay long in the PS-cache, and after that the link doesn't work (someone correct me if I'm wrong about this).
Established Member
But that is my whole point dgruss--the bridges do not act as another form of evidence where there is no other independant means by which to determine that there is, in fact, interaction. The problem, again, is that I am unaware of any that are listed by the Arpian group that are close enough for imaging of an acceptable standard candle to occur (at least in the absense of a SN1a in a bridge, which has not, AFAIK, been imaged).
So bridging will never be accepted as stand alone evidence of interaction between low and high redshift objects. In the absense some other empirical evidence, and especially in the absense of some empirical evidence that the Hubble standard is incorrect, they will simply remain (to mainstream scientists at least) coincedences of line of sight alignments in 2d pictures.
To try and put it another way, it is not enough for you to point to {coincidentally aligned} objects that are so distant as to be unusable in this discussion.
I'll come back to this.
All galaxies that are close enough for us to image clearly show evidence of ongoing "cannabalism", with the closer galaxies (M31 for eg) showing evidence of several instances of merger. In mainstream, it is merger that creates the gravitational forces which drag out bridges and tails. In the Arpian view, as I understand it, it is the ejection of a newly formed galaxy that creates these artifacts.
So, we have optical evidence of nearby past and present galactic merger. As far as I am aware, there is no optical evidence of nearby galactic ejection, past or present. Why? What is so special about this region of space that not one single member of our local group shows any evidence of an ejection event?
They are almost entirely useless in the absense of individual star resolution because if the stars of the bridge cannot be resolved, there is no other empirical means (short of redshift measurement) to confirm the distance of the object. (Well, a caveat, if a SN1a is seen in a bridge, it will be quite useful) The whole issue is that it does not go beyond "looks like". A recent galactic merger can easily throw out a long streamer of stars, which can "look like" a bridge. Look at M51, or NGC5291 or several other clear ongoing galactic mergers. And I disagree with your interpretation of NGC7603. There are 2 galaxies at the right distance, close to each other, and the bridge between them seems to be at the same distance. Itn my view, the other 2 are aligned only by chance, and only appear to be part of the dance.
That's just it, I think the optical wavelength is the clearest, whereas the other wavelengths have some bleedout. I am looking into this aspect.
Lost me here dgruss--NGC1232 &1232A have close togeather, bith at ~ 70Mly away. Oh, wait I think you must be talking about the z=0.1 RS object showing through gap in the upper arm due north of the galactic centre? (photo) I do not see interaction here (between 1232 and the object I mention), and I do not believe the object is in front of the main galaxy either--it looks reddened by the dust of the main galaxy which its light has to shine through.
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I'm note sure I understand what you are looking for here, nor why. If two galaxies are close togeather, their gravitational fields will likely cause interaction. Such interaction could be expected to pull out streamers of stars, or a bridge. I can't imagine a scenerio where such an interaction would not occur??
Established Member
I beg to differ on a couple of points. First of all, look at this local galaxy.
http://www.astro.princeton.edu/~rhl/...es/M51-4x4.jpg
While mergers are common, it has been fashionable to call every interaction a merger, despite the fact that many companions appear to have been ejected, distorting the host in the process. It is not the Arpian view that every interaction is an ejection event, although many are. It is the Arpian view that many of these interactions that are commonly characterized as mergers are in fact the opposite. The narrow, well-defined tidal stream from NGC 7603 to NGC 7603B is a textbook example of what an ejection can look like. This is supported by the bright pointed jet of material extending into the tidal stream from the host galaxy.
It is possible for a merger in progress to result in the apparent convergence of a companion and the end of a spiral arm of the host, and I presume that lots of people look at M51-type systems in just this way. The fact that there are so many of these systems (with companions located right at the end of a distorted arm of the host spiral) argues convincingly for the ejection hypothesis and against the interpretation that these are all mergers.
Order of Kilopi
Yes - the bridges are a very clear form of evidence for interaction. If the objects are interacting, they are at the same distance. There are cases in which the object was described as interacting - and then later redshift measures have showed a difference in redshift that is too large to be a peculiar motion. Obviously before the redshift measurement the bridge was considered a form of evidence. Then the bridge is dismissed as evidence for interaction after the redshift is measured.
This is a bigger problem for the mainstream. If you look again - you've been provided with other means besides the bridges of tying all this together. The objects in question are typical starbursting galaxies or show enhanced star formation - another sign of interaction. L-C&G pointed out that the equivalent widths of the spectral lines for the HII galaxies better fit the expected EW-luminosity relation at the NGC 7603 distance.
So on what basis - besides redshift - do you conclude that these are not interacting systems? I'm waiting for somebody to provide anything in that regard.
The problem is made worse by the fact that most of these bridge instances involve dwarf or disturbed galaxies that don't lend themselves to a systematic study via redshift independent distance indicators.The problem, again, is that I am unaware of any that are listed by the Arpian group that are close enough for imaging of an acceptable standard candle to occur (at least in the absense of a SN1a in a bridge, which has not, AFAIK, been imaged).
Other empirical evidence has been provided. Not to mention the mainstream now finds themselves in the position of explaining the origin of these bridges - since in most of these cases there is not another candidate perturber nearby. And as has been pointed out several times - where are the near misses?So bridging will never be accepted as stand alone evidence of interaction between low and high redshift objects. In the absense some other empirical evidence, and especially in the absense of some empirical evidence that the Hubble standard is incorrect, they will simply remain (to mainstream scientists at least) coincedences of line of sight alignments in 2d pictures.
More than alignment has been pointed out.To try and put it another way, it is not enough for you to point to {coincidentally aligned} objects that are so distant as to be unusable in this discussion.
The tails and bridges are not permanent fixtures (see Toomre&Toomre). There are many more galaxies without bridges and tails than with those features. The bridges are signs of recent interaction.All galaxies that are close enough for us to image clearly show evidence of ongoing "cannabalism", with the closer galaxies (M31 for eg) showing evidence of several instances of merger. In mainstream, it is merger that creates the gravitational forces which drag out bridges and tails. In the Arpian view, as I understand it, it is the ejection of a newly formed galaxy that creates these artifacts.
Is M-31 a Seyfert? Or a starburst galaxy? Is the Milky Way a Seyfert? Or a starburst galaxy? No. But the nearest galaxies that are - NGC 5128 and M-82 are cases that show evidence of ejection. Another point that is frequently lost as these discussions proceed - most of Arp's examples involve active galaxies or ScI galaxies.So, we have optical evidence of nearby past and present galactic merger. As far as I am aware, there is no optical evidence of nearby galactic ejection, past or present. Why? What is so special about this region of space that not one single member of our local group shows any evidence of an ejection event?
The evidence does go beyond "looks like". You need to go back and look at the evidence I've discussed, others have discussed, and has been discussed in the papers that have been cited - including non-Arpian papers. The fact remains that the only evidence presented here against interaction is the measured redshifts. We've presented evidence for interaction on top of the bridges.They are almost entirely useless in the absense of individual star resolution because if the stars of the bridge cannot be resolved, there is no other empirical means (short of redshift measurement) to confirm the distance of the object. (Well, a caveat, if a SN1a is seen in a bridge, it will be quite useful) The whole issue is that it does not go beyond "looks like". A recent galactic merger can easily throw out a long streamer of stars, which can "look like" a bridge.
The other two objects are HII galaxies - star forming galaxies - a sign of interaction. LC&G used pointed out that their equivalent widths support them being at the NGC 7603 distance. And turbo-1 has pointed out several times that they elongate back toward NGC 7603 and NGC 7603B.Look at M51, or NGC5291 or several other clear ongoing galactic mergers. And I disagree with your interpretation of NGC7603. There are 2 galaxies at the right distance, close to each other, and the bridge between them seems to be at the same distance. Itn my view, the other 2 are aligned only by chance, and only appear to be part of the dance.
But I'm glad you agree that there are 2 galaxies at the same distance in this instance connected by a bridge because the 2 galaxies are NGC 7603 (8700 km s-1) and NGC 7603B (16,200 km s-1).
I'm not following you on this one Duane. NGC 1232 has a redshift of ~ 1600 km s-1 and NGC 1232A has a redshift of ~6400 km s-1. The high resolution imagese of the z=0.10 galaxy (NGC 1232B) are published in Arp's Catalog of Discordant Redshift Associations and show that the object has a filament extending back toward the spiral arm of NGC 1232.Lost me here dgruss--NGC1232 &1232A have close togeather, bith at ~ 70Mly away. Oh, wait I think you must be talking about the z=0.1 RS object showing through gap in the upper arm due north of the galactic centre? (photo) I do not see interaction here (between 1232 and the object I mention), and I do not believe the object is in front of the main galaxy either--it looks reddened by the dust of the main galaxy which its light has to shine through.
As for reddening, this is an argument I pointed out a long time ago that nobody had any interest in. NGC 1232B is not significantly reddened.
Order of Kilopi
Its simple - and you've illustrated my point. When two galaxies interact they will create bridges and streamers. If the objects have the same redshift they are automatically interpreted as interpreted as interacting galaxies and the bridges are interpreted as resulting from that interaction.
But when the redshifts of the two galaxies are different, then the bridges are dismissed as evidence for interaction by the mainstream. The problem with this is that then there is not explanation for the bridge - eg NGC 7603. Where is the galaxy that produced this bridge? NGC 7603B is the obvious candidate - but it has twice the redshift of NGC 7603. There is no other candidate.
Established Member
In the case of NGC 7603, I recently pointed out a number of independent indicators of interaction. It's not just the existence of the bridge, although the bridge is a strong indicator of interaction.
NOTE: more astute observers may notice other evidence for interaction when examining the images of this system. These are IMO the most obvious observations supporting the case for interaction.
As dgruss23 pointed out, if you insist that NGC 7603 and NGC 7603B cannot have interacted to create the bridge, you're stuck, because there is no other viable candidate for gravitational interaction anywhere near the system. Even more important, since bridges are dynamic artifacts, and not permanent structures (Toomre and Toomre), the companion galaxy that caused the bridge should still be very close by. It is - it just happens to have excess redshift.
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Your final question in this section got me looking around for deep exposures of local galaxies, and I found this nice example with a mouse-over feature that lets you view the host galaxy in optical at normal exposure levels. Please open the link in a separate window, so you can look at the image while following the discussion below:
http://www.aao.gov.au/images/deep_html/n4321_d.html
What do we see here? This is a very deep image of the M100 system. The dwarf elliptical at the 11:00 position is NGC 4323, which has an excess redshift of ~230 km/s. I had half-expected to find that NGC 4323 would be located at the termination of the NE spiral arm. I was surprised (although pleasantly so) to discover that instead NGC 4323 lies on the terminus of a tidal stream that extends straight back toward the center of M100. The NE spiral arm, which is bifurcated, does not seem to have been disrupted by the passage of the DE galaxy, indicating that the ejection angle is significantly inclined WRT to the plane of M100's disk, and the tidal stream is either seen in projection in front of the spiral arm or is in back of the arm and seen through it.
Yet another bridge indicative of interaction and apparent ejection. In this case, the redshift difference is small enough that even the most conservative cosmologists should have no trouble accepting the interaction, even if they insist that the parties are "merging" instead of separating.
Now, this is a great image and it was produced intentionally as a deep image to show faint detail. You can find other nice images on-line, though, like the SDSS survey pictures, load them into Photoshop and increase the contrast to bring out the faint detail. I could see a hint of the tidal stream when I did this with a picture of M100 and sought out a deep exposure to confirm that it was real, and not an artifact of image processing.
EDIT: Duane, it occurs to me that there are perhaps a lot more ejection events locally than we currently accept because we are spoiled by the Local Group. Telescope time is precious, and when we can get a beautiful image of a bright nearby galaxy without going to deep exposures, we will miss bridges like this one. With really faint distant objects, we are forced to resort to deep exposures and may be more likely to pick up the bridges. Selection effect...
Last edited by turbo-1; 2006-Apr-08 at 08:21 PM.
Established Member
Yea, M51, The Whirlpool Galaxy. I already mentioned it. I don't see what point you are trying to raise by linking to this image. The Whirlpool is a classic example of an interacting couplet of galaxies. Long streamers of stars are evident all aropund this pair, indicating an ongoing interaction leading to a probable merger in a relatively short time.
Furthermore, it is thought that M51 is, or is becoming, a Seyfert. Is it not this type of galaxy that Arp et al feel will "calf" (or whatever you call it) new galaxies? Regardless, M51 is often held up as an example of sudden flaring of the SMBH resulting from a recent close encounter.
So where then is an example of a galaxy where the ejected mass is still embedded in the host, causing the massive distortion of the host that would be expected by the sudden ejection of such a mass? How, pray tell, would the central bulge remain pristine?
So I am clear, are you saying that the ejected body leaves the system which calved it by way of a spiral arm?
Established Member
No, it is not at all black-and white like that. Ejections more or less in the plane of the disk result in this type of interaction, the morphology of which Arp simply called "M51 type" in his catalogs of interacting galaxies. It is also often the case that an ejection is NOT along the plane of the disk, like in the image M100 and NGC 4323 that I just linked. In this instance, the tidal stream is seen in projection either in front of or in back of the NE spiral arm of M100.
Established Member
dgruss, you need to take a closer look at your "evidence " for the group around 7306. First of all, there are 4 objects, an HII galaxy at z=0.22, a QSO and a second HII galaxy at z=0.19, and a quiescent galaxy at z=0.12. The streamer (or bridge, if you prefer) material is also at 0.19, suggesting interaction between the QSO and the HII which are at that same distance. The fact that there is another, fainter, HII galaxy in the group does not necessarily denote interaction with the first pair. (albeit, it doesn't preclude it either.) So, in short, given the "bridge" intersects 2 fainter HII galaxies and also intersects the QSO, it seems to be a very poor example for you to rely on.
Established Member
Aha! Isn't this what dgruss23 was asking for? A system with a "bridge" that goes nowhere?
Of course, the system that caused the tail / bridge to be created in the first place is probably a bit further away (I mean to "left" or "right" inj picture, not farther wrt Earth) and has left the interaction behind, but it could also be that such a tail can start on its own (though that seems more unlikely). Anyway, what this seems to show is that you can have a tail without an end galaxy, and this in turn shows that in some cases, what looks to be the end galaxy is simply a chance alignment.
I don't want to claim for now that all such "bridges" with different redshift are change alignments, that's too easy, but we have to keep it in mind. Chances of a chance alignment somewhere in a bridge are of course higher than at the very end of the bridge.
You're quite right, thanks! I hadn't checked it, but these seem indeed to be temporary links. I'll try to remember it.Btw. your link didn't work for me. It might be better to give links to the abstract page (here's the abstract page of the paper in question), as I think that the PDFs don't stay long in the PS-cache, and after that the link doesn't work (someone correct me if I'm wrong about this).
Established Member
Yes, obviously.
Well, be careful here. That something initially "looked like" that does not lead to the conclusion that it was. Thats why closer looks were taken.
It's the same "looks like" argument that has been made too many times when referring to 2d photographs.
I'm out of time here, but I'll come back to the subject soon.
Established Member
I'm not sure that this qualifies as a misalignment - as I have said earlier (at least a couple of times) given the peculiar motions, rotations, etc, of the host and companion, the alignment is very good.
There are lots of other fuzzy objects in the field, and as you will see if you scroll back a few posts to my post on M100, bridges are not always fully apparent at any given exposure, and it is necessary to go deep to see the bridges. In the case of NGC 7603, which is very distant and faint, it might be necessary to go very deep to verify the bridges that you observe and to see if any of the local fuzzies might be responsible for them. If Sharp's comments regarding the resistance to his observations of this system are true (and I have no reason to believe they are not), it might be very difficult for a researcher to be allotted the time required for very deep imaging of this field.
It is true that the luminous envelope surrounding the system exhibits a significant extension in the arc of the spiral arm. The narrow, very luminous tidal stream does not extend beyond NGC 7603B, however, in contrast to this example:
http://www.astro.princeton.edu/~rhl/...es/NGC5218.jpg
Thank you for the work that you have done. It is much appreciated.
Established Member
Yes, and probably that's why it has a line alignment of higher redshift galaxies (pp. 14-15 of the linked paper).
On ejections in the local group, you might notice that the paper linked above also discusses M31 and M33. Here is another paper discussing M31 and this paper discusses quasars around M33.
If we consult the Narlikar-Arp variable mass theory, then there's no huge mass involved in the ejection initially. The ejection starts with almost zero mass particles. I've outlined the ejection mechanism in this post.
Aren't you talking about NEQ3, not NGC 7603? (At least the redshift values you mention suggest that.)
Established Member
Yes, it would be that if there wouldn't be obvious cause for "interaction". It would just make you wonder what process created that huge "arm" if there's no interaction.
It seems that NGC 772 system is commonly held as an interacting system, so you're probably correct.
Some kind of quantum effect perhaps? You know, this arm has a certain, but very low, probability to be considerably longer than other arms, and that probability has came true in NGC 772 system.
Yes, it could be that some cases are chance alignments, even if most alignments would represent a true connection between discordant redshift galaxies. But that's a good point, NGC 772 is an interesting example of the tail ending at empty space.
That is what we are probing right now. If they are chance alignments, then there should be considerably more cases missing the discordant redshift object, because chances of the tail missing the discordant redshift object completely are much higher than the tail hitting the object (let alone the chances of only the end of the tail hitting the object).
Order of Kilopi
No Duane, it is you that needs to take a closer look. You just described the NEQ3 system, not the NGC 7603 system - but you're referring to it as NGC 7603.
And in your post yesterday you suggested that there was a bridge connecting two objects that were at the same distance and that the two objects in the filament were background galaxies:
The two galaxies you are saying are at the same distance are NGC 7603 and NGC 7603B. NGC 7603 has a redshift of z=0.029 and NGC 7603B has a redshift of z=0.057. Since it is clear that you think these are chance superpostions you must not actually think these two are at the same distance - but had your facts mixed up on the system. Unless of course your description of "NGC 7603" above was meant to be a description of NEQ3??? In either case, it is not I that needs to get my facts straight.
What evidence has led to to conclude these other objects only appear to be part of the dance?
Order of Kilopi
"No" to question #1 and "not exactly" to question #2. What I'm looking for is an instance in which there is a "bridge" between two objects - yet the mainstream interpretation is that the "bridge" is not a sign of interaction. We could make that easier by expanding it to tails as well. These features are always interpreted as the result of interaction.
In the case of NGC 772, the preprint you linked to says this:
NGC 770 is within 5 arc min of NGC 772 and has a redshift that agrees within 15 km s-1 of that of N772, so that galaxy would be your likely perturber in the mainstream view. So again we see the mainstream interpetation is that these features are the result of interaction.NGC 772: Clear disruption signatures can be found in the spiral arms of this galaxy, which are likely due to interactions with some of the satellites detected around it (See Zaritsky et al 1997).
You cannot have a tail without interaction - in the mainstream view. Arp would say you can have these features as a result of ejection - but that's another whole issue.Of course, the system that caused the tail / bridge to be created in the first place is probably a bit further away (I mean to "left" or "right" inj picture, not farther wrt Earth) and has left the interaction behind, but it could also be that such a tail can start on its own (though that seems more unlikely). Anyway, what this seems to show is that you can have a tail without an end galaxy, and this in turn shows that in some cases, what looks to be the end galaxy is simply a chance alignment.
Yes and that is what is missing in these high redshift/low redshift alignments. The bridges always "appear" as bridges and never appear to pass over the higher z galaxy. Think about all the possible ways a tidal tail could be pulled out and pass near a true background galaxy. Everyone should just form a mental picture of that process. Why is it the only scenario we are seeing is the scenario in which the tidal tail "accidentally" terminates at the position of the "background" galaxy. The odds of other configurations not observed (if it is accidental) significantly outnumber the odds of the observed configurations.I don't want to claim for now that all such "bridges" with different redshift are change alignments, that's too easy, but we have to keep it in mind. Chances of a chance alignment somewhere in a bridge are of course higher than at the very end of the bridge.
Order of Kilopi
The point is that bridges are always taken as evidence of interaction - until the redshifts are found to be different. Does the mainstream have any other criteria? I have seen any yet.
And we've explained numerous times how the evidence goes beyond "looks like". When you get a chance, I would like to hear your thoughts on that other evidence.
Established Member
I mentioned this before, and it should probably be factored into your consideration of real vs chance alignments of companions with tidal tails:
If these are merely chance alignments, there should be a number of examples in which the tidal tail ends exactly in back of a closer, lower-redshift dwarf galaxy, mimicing the appearance of the M51-types. Where are these examples? It seems that in the examples we have, the smaller companion is at about the same redshift as the host (in which case, mainstream astronomers readily accept the bridge as evidence for interaction) or is redshifted with respect to the host (in which case the mainstreamers deny that the bridge is evidence for interaction). Where are the blueshifted companions in these M51-type examples? I don't mean blueshifted to the extent that can be explained by the peculiar motion of the companion WRT the host - I mean blueshifted enough that mainstreamers will insist that the galaxies cannot be interacting (perhaps 1000 km/s or so).
If we cannot find a population of M51-types with this configuration (accidental alignments with tails ending on significantly blueshifted "companions"), does not this argue strongly for the view that smaller companion galaxies are systematically more redshifted than their hosts? Is there an alternate interpretation? I have not been able to formulate one that holds water.
Administrator
I'm checking on something implied above. I emphasized "exactly". Are there any examples where the physical alignment of the end of the tidal tail "exactly" aligns with a high redshift Quasar? I'm guessing that in any case where an image seems to show such alignment, that a deeper image would show the tidal tail (or shock front, or ejection streamer) as extending beyond the object, even if the object were in superimposed against the stream.
That being said, I am also interested in the actual point of turbo-1's post. Do we have a catelog of interacting galaxies in which we record the redshifts of the larger vs. smaller galaxy? Is it in fact the case that the smaller galaxy always has a higher red shift as turbo-1 implies? I don't know the answer, but if the assertion is correct, I agree it is pretty meaningful.
Forming opinions as we speak
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