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One other wrinkle - for many years, Sandage et al (using standard candles like HII regions, Cepheids, and SN1as) got consistently lower estimates for the Hubble constant than Freedman et al. If galactic spectra are contaminated by an intrinsic redshift component, this is exactly the type of trend you would expect to see.Originally Posted by dgruss23
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Yes, Sandage et al attribute the higher H0 value obtained by Freedman et al as resulting from Malmquist Bias. For Malmquist bias to have a significant effect there must be large intrinsic scatter in the secondary distance indicators. Freedman et al find small intrinsic scatter in the distance indicators while Sandage et al find large intrinsic scatter. There is a big difference in their methods. Sandage uses Hubble distances (assumes a tight Hubble relation) to calibrate the distance indicators whereas Freedman et al use primary distance indicators and cluster samples.
The large scatter observed by Sandage when calibrating from Hubble distances is expected if there is significant error introduced into the Hubble distances from contamination by intrinsic redshifts.
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Historical note: According to Keel, http://www.bautforum.com/showthread.php?t=41089 , Sandage argued long and loud for his shorter distance scale, but finally threw in the towel and accepted as a fact that galaxy evolution skewed his distance estimates. Me thinks he gave up too soon.
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OK, here is the refined list of Hc velocity differentials for all the A-M associations in the M51-type chapter. The Arp associations were selected visually based on the following criteria by Ari and dgruss23 with no input from me:
(1) Main galaxy is a spiral
(2) Companion is less than 50% the diameter of the parent
(3) Bridge (1) connects from a spiral arm (either the Arm or an extension of the arm) to the companion or (2)nearly connects but clearly arcs toward the companion. Perhaps we could break these down into M-51bc and M-51 bnc where bc is "bridge connects" and bnc is "bridge nearly connects".
(4) Connection is from the parent galaxy to the main body of the companion galaxy and not some extensions from the companion.
We now have a sample of 23 M51-types selected based on stringent optical criteria. Of them, 4 associations contain a large host galaxy with excess redshift relative to the small companion, and the redshift (expressed as Hc V) averages -176 km/s. In the remaining 19 associations, the smaller companion has the excess redshift, averaging 5039 km/s. The data set is still rather small, but continues to exhibit the strong statistical biases shown in previous data sets. In this data set, the companion is 4x as likely as the host to exhibit excess redshift, and the magnitude of the redshift differential (when the small companion has the exess redshift) is 29x larger than when the host has the excess redshift.Code:A-M # excess V..km/s 0324-524 -260 0523-400 -156 73 -108 86 -96 85 5 1108-300 18 82 39 1304-333 81 58 92 0327-285 128 0639-582 145 88 165 2256-254 324 1353-272 354 2105-332 361 0500-620 780 2100-381 1555 2256-304 2352 0037-305 2627 92 7898 0058-402 9642 67 11230 2052-221 36526 Host ave -176 Comp ave 5039
I want to thank both Ari and dgruss23 for their work in culling the list of M51-type candidates. I felt it was important that I not do it myself, since I had already extracted the differential Hc velocities for the data set. They were pretty ruthless in following the protocol laid out above, and they had some back-and-forth disussions about why particular associations should or should not be considered M51-types. I appreciate their efforts.
To keep things in perspective, the M51-type associations are not the only types of bridges we are discussing currently, but they are a sub-set of bridged associations that seems to exhibit some pretty eye-opening characteristics WRT intrinsic redshift. Other interacting systems may or may not have such interesting properties, but even a null result tells us something. At this point, we do not know what mechanism drives the redshift differential, but we may be able to glean some clues as we build our data-sets and sort them on morphology, size differential, type of interaction, strength of interaction, etc.
If anybody has a suggestion about some criteria that we could add to sort the data-sets, we will gladly add them to the pile that we are culling now. Some interesting ideas might lack observational data (even the redshift data is missing throughout most of the A-M catalog and much of the Arp's first catalog!), but I would like to hear of them.
Thanks
Last edited by turbo-1; 2006-May-04 at 11:51 PM.
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Could be true. If intrinsic redshift plays any role, the Hubble parameter is over-estimated.
Last edited by turbo-1; 2006-May-04 at 11:54 PM.
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However, we still haven't incorporated cases from VV-catalogs (second VV-catalog is still in it's data collecting phase). I earlier gave a list of 10 cases where few were already in turbo'1's list, and then there were some cases I wasn't sure about. Now we have established the criteria for M51-types described by turbo'1 above (and originally suggested by dgruss23), and it means that there are more cases entering this group from VV-catalog, especially to M51 bnc subgroup. So, we have to through the candidate cases from VV-catalog, and then see where this trend settles. I have to say that the trend is amazingly strong in turbo-1's cases.
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It will be interesting to see how the VV-catalog M51-type examples trend, once you get them collected and identified.
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Are these galaxies connected?
Everyone is entitled to his own opinion, but not his own facts.
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Does the image above meet criterion #4?
Everyone is entitled to his own opinion, but not his own facts.
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What the heck is the long straight line coming from the little galaxy on the right going down and to the left? Is that a photographic defect? What is the source of this image?Are these galaxies connected?
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I have no idea.
This is from the Arp-Madore Catalog.
Everyone is entitled to his own opinion, but not his own facts.
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If it is something seen in other images, it is a very strange feature. If it is an artifact of the image, it kind of brings every straight line seen in the Arp-Madore catalog into doubt. What galaxy is the main one in this image?
Forming opinions as we speak
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This is AM 2052-221, the last on the list in Turbo's post #1624 above. With a velocity differential of 36,526 km/sec (z differential of 0.12), this is three times the next highest differential on the list. Of course, this would tend to have a significant effect on any "averaging" one did on the data set.
Everyone is entitled to his own opinion, but not his own facts.
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I would say that there is no connection based on that image. I would look for another image for this system before making any conclusions. Now as I have been looking at the VV-catalog, there has been many cases where I need to look at many different images of the system in question before I can make any conclusions about it (for example when trying to decide is there a bridge or not). But based on that image, I would say that there is an interaction tail coming out of smaller companion, spiral arms of the bigger galaxy point to wrong direction for that to be end of a spiral arm of the bigger galaxy. After looking at NED-images of this system, it seems that there are no better available (at least in NED). turbo-1, you might want to consider that system again, it might not be a M51-type. Good catch, Cougar! Keep them coming...
We have to remember that these images published in the Internet might be scanned from some paper-copy of the catalog, or from copy of copy, so I wouldn't be surprised if there are some artifacts in the images. Anyone here own a copy of the Arp-Madore catalog? If someone does, it would be interesting to know if that straight line is there as well.
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Regarding AM2052-221 - the galaxy was discussed in more detail here . Figure 1c is a deep exposure of the system and in that image the filament reaches back very close to the disk. The NED image is lower resolution and is useful to show the inner disturbed ring structure of the parent galaxy. Based upon the deeper image I would keep this one as an M-51 class - although I'm in favor of deep R-band imaging being performed.
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I see what you mean. The filament seems to almost connect in that image. But what troubles me with this, as I already mentioned in my previous post, is the direction of spiral arms of the host galaxy, visible in the image Cougar posted, they are in opposite direction than this supposed arm. That suggests to me that this filament is not an arm of the host galaxy.
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There is a range of morphology in the spiral arm structure. In this galaxy the spirals are really distorted rings. In some of the others the companion is on the end of a normal curving spiral arm and then in others the spiral starts out normal and curving, but becomes straight and elongated toward the companion. Until these Arp objects are imaged with modern CCD imaging technology there will be uncertainty in what we are looking at in some cases.
I would agree that the filament is not an arm of the host. Actually in NGC 7603, the filament is inside an arm of the host, so if we're talking about an ejection mechanism, I would expect some variety in the configurations.
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Every object in the catalog should be re-imaged. But the cases being discussed are much more distinct features than this line. There are not many cases where the existence of the feature is really disputed.
But that might be a worthwhile project. If any mainstreamers are interested. Go through the Arp or AM catalog and look for galaxies that you think have features that are possibly just plate flaws. It wouldn't take that long using the NED versions of the catalogs.
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You are correct that it does have an effect on the average. It is reduced to 3290 km s-1 without it. But I don't think the average is the important number - the trend is. Of 23 examples in only 4 cases the companion has the smaller redshift. In 19 cases the companion has the larger redshift. That is a discrepancy that needs to be explained.
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Yes, the UK Schidt plate is much deeper than the plate in Arp-Madore (I do have the book), and it is the exact same plate the Cougar linked to, with the same straight line. I would like to find another plate of this area - that object with the thin line is elongated exactly in the direction of the line - I wonder if someone missed a serendipitous comet discovery here?
dgruss23, if you will look at Figure 1C in the Arp paper you will see a luminous knot where the tail from the companion meets the fringe of the host. We should see if there has been any X-ray imagery of this system. I'm curious to see whether that little body is a ULX.
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Note: definitely not a comet - the elongated object shows up on two other NED images, but the streak does not. Of course many of the objects that show up clearly as fuzzy spots (galaxies) on the AM plate do not show up at all on the other NED plates, and both are quite grainy, so it is not suprising that the streak would not show up. We need better imagery of this system (and many others!)
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You ever seen Blow Up (1966)?
Synopsis: Taking photographs of a couple making love proves deadly when the photographer enlarges the image and discovers murder. The film and pictures are stolen from his studio and the body vanishes. In this elegant balance of deciet and trickery, the photographer must question the reality of what he has actually seen.
Everyone is entitled to his own opinion, but not his own facts.
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IMO this entire bridges discussion has been an example of questioning the reality of what is being seen. The thrust has been whether or not the bridges evidence goes beyond it "just looks like".
But obviously each individual case requires its own thorough study - and until such observations are made there can be no evidence that goes beyond "just looks like". That is why observations of they type done with NGC 7603 are so critical. Similar observations need to be done for other systems.
But now I want to see "Blow up"! I suppose that's not one commonly found on the rental shelves?
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I strongly agree. Let's say that part of the redshift of an object is in fact intrinsic. Then it isn't moving so fast, isn't so far away, isn't so large, and isn't accelerating away from us so fast. So dark energy might not be needed after all. And those galaxies in clusters aren't really moving so fast, and separating from each other as rapidly. So dark matter might not be needed to explain their motion. We may not even need Inflation in the early times. We could have solid observational evidence for bridges between objects with high redshift differential and only have to figure out what is causing the evident intrinsic redshift. I think many scientists and educators in this field would welcome such a change of scope, if it was backed by sound evidence.
TomT
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An alternative universe. This could be a great setting.... for a science fiction story.
Everyone is entitled to his own opinion, but not his own facts.
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You conveniently left out the last few words of my statement, namely "if it was backed by sound evidence". This is what will indicate if the rest is science fiction or not. Notice, I did not say the BB is wrong, only that it may need a bit of tweaking.
TomT
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Maybe not, though it was an extremely influential film at the time (in cinematographic, not astronomic, terms...). You can find a DVD of it for around 12 USD on e-Bay, for example here.
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Indeed. Do we not need some kind of "alternative" if the rigourous work done by dgruss23, Turbo-1 and Ari Jokimaki on M51-type bridges has any meaning? I too have noted that the regular mainstream contributors to this thread have been surprisingly absent since the start of the M51-type bridges discussion. Shouldn't this be taken as some kind of admission concerning a possible "alternative" interpretation of at least a component of the redshift observed in certain inter-galactic associations (even if we do not yet understand the mechanism behind the observations)?An alternative universe.
Why "fiction"? If the confirmation of an intrinsic component of redshift can indeed help astronomers to set aside once and for all the embarassment of having to carry on proclaiming the existence of those vast quantites of elusive "DM" and "DE" FAIRIEDUST which seem to be increasingly required by belief in the standard interpretation of redshift, then we shall simply be moving away from "The Emperor's New Clothes" towards, not a "science fiction story", but a good science story. It will not be too soon.
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Given that you softened this by using the word possible, I'd say that for myself the work so far has shown that there is a difficult issue to answer here. I am not embracing intrinsic redshift, but it is clear that I need more information before I can say this is a non-issue. I am very happy to see the comparitively fair analysis of some of this data by Arp proponents, making this case less clear-cut, but clearly the data needed to really give this a fair look is hard to find, or currently non-existant, and yet, within the grasp of today's instruments.
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That's the question: Does it have any meaning? Is it really rigorous? Is the sample size sufficient to reach any conclusions? Is the selection of this particular sample population unbiased?
Not in the slightest.
Everyone is entitled to his own opinion, but not his own facts.
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