A long time ago in a thread far, far away, some of us were discussing apparent interactions between astronomical bodies with different redshifts. The "More from Arp et al" thread was initiated by antoniseb, and during the discussion he asked (post 1320):

I won't go into the details here but my first crack at the study yielded some interesting results, summarized here:
More from Arp et al.

Very soon, I was joined by Ari and Dave and we decided to study galactic associations that fit the M51 archetype. It took us a couple of years to assemble the catalog and gather the data for the tables (thanks Ari!) and get the paper ready for publication. The paper has been accepted for publication by Astrophysics and Space Science - a peer-reviewed journal published by Springer. We have made a pre-print available on arXiv:
http://arxiv.org/abs/0805.1492

The data tables (too large to publish in print) and annotated images of every galaxy association in the M51 sample and the possible M51 sample are available on our web site:
www.jorcat.com/

We would like to acknowledge the generosity of Mike Petersen, who provided us with a domain name, server space, and his web-design skills in building and maintaining the site. It is much appreciated. Thanks to antoniseb for asking the innocent-sounding question that launched this project.

To anybody with access to decent-sized scopes with spectrometers - look at the redshift numbers of the companion galaxies. Fewer than 20% of them have any published redshifts. Given the potential value of this catalog for the study of galaxy morphology, dynamics, triggered star-formation, etc, it would be wonderful to see these gaps filled. Anybody up for it?

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The ether of general relativity therefore differs from that of classical mechanics or the special theory of relativity respectively, in so far as it is not 'absolute', but is determined in its locally variable properties by ponderable matter.

Albert Einstein, "On the Ether", 1924

Congrats to you, Ari and Dave. That's no small feat! I can't imagine the hours of work that went into this.

A giant step for BAUTkind!

Thank you for the kind words. A prominent observational astronomer told us that we were crazy for taking on such a large project in a non-academic setting. He said that since we had no grad students to enslave, we would have to enslave ourselves. He was right!

There's much more to be done, even with the limited spectroscopy available to us on the companion galaxies, and our second paper is already in the works.

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The ether of general relativity therefore differs from that of classical mechanics or the special theory of relativity respectively, in so far as it is not 'absolute', but is determined in its locally variable properties by ponderable matter.

Albert Einstein, "On the Ether", 1924

Congratulations to all of you!

If you weren't already aware of it, you might be interested in what Galaxyzoo is currently working on. A lot of potential mergers were found during the first stage of galaxyzoo, and they are now doing more detailed classification of these systems. They have a PDF tutorial available if you want to take a look. Eventually there will be a catalog published with these results, which you might want to compare to.

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"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

I'm quite interested in the Galaxyzoo project. I have attempted to participate through the classification process, but always run into an error. I emailed them with no resolution. You wouldn't think that after staring at multi-band IRSA imagery for hours every day, I'd want to classify galaxies for them, but it seemed like a worth-while endeavor. On behalf of Dave, Ari, and myself, thank you for the kind words.

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The ether of general relativity therefore differs from that of classical mechanics or the special theory of relativity respectively, in so far as it is not 'absolute', but is determined in its locally variable properties by ponderable matter.

Albert Einstein, "On the Ether", 1924

What error were you getting, and during what stage of the process? Also, when did you try it? There were some bugs early on that have since been smoothed out.

Staring at galaxies is always fun!

Their first two papers have been submitted, if you want to see how it is going.

A thought for the three of you: do any of the public telescopes (like SLOOH) have access to spectrographs of any kind? If all you care about are redshifts, you could make do with quite low resolution spectra, so long as their wavelength calibration is decent.

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"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

Thanks for the suggestions, parejkoj. I'll have to alert my co-conspirators to the possibility of using publicly-available instruments. Magnitude may be a limiting factor, since many of our companion galaxies are tiny and faint.

The Galaxy zoo error is:
"An Error has occurred

Galaxy Zoo has experienced a technical difficulty. The problem has been logged and we are looking into it. Please make sure you have cookies and javascript enabled. You can keep browsing and classifying but if the problem persists check back soon as we're sure to have the issue resolved."
The error has never resolved, and it appears every time I try to classify a galaxy.

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The ether of general relativity therefore differs from that of classical mechanics or the special theory of relativity respectively, in so far as it is not 'absolute', but is determined in its locally variable properties by ponderable matter.

Albert Einstein, "On the Ether", 1924

You and I conversed a bit through PM in the last day or two, and I congratulated you there, but let me do it publicly too. Well Done.

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Forming opinions as we speak

Thanks antoniseb. When you posed your question, I was unsure if I could pull together the information that you asked about. Thankfully, Ari and Dave jumped in. They are both far more organized and detail-oriented than I am and they both added organization, structure, and discipline to the project that greatly enhanced the quality of the work. We've got a lot more ahead of us, and the next paper will contain another author whose name you're sure to recognize... Thanks again.

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The ether of general relativity therefore differs from that of classical mechanics or the special theory of relativity respectively, in so far as it is not 'absolute', but is determined in its locally variable properties by ponderable matter.

Albert Einstein, "On the Ether", 1924

Huh... I looked around in the forums, and there were a few other people who had similar problems, some of which got resolved after updates, some apparently not. Have you tried creating a new account, or posting in the forum? I'm sorry I can't help you more than that.

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"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

Congratulations!

I've very briefly browsed one of the datafiles, and I think there is a way for you do quite a bit of work without any spectroscopy.

Many of the companion galaxies are faint enough -- fainter than 14'th mag -- that they might be measured by the SDSS. Now, the SDSS only covers one quarter of the sky, so it will have measurements for only some of your candidates .... but it's a sizeable fraction.

If the SDSS gives you magnitudes of the companion galaxies in multiple passbands (it observed in five passbands across the visible), then you can use the colors of the companion galaxies to estimate their redshifts. There are a number of slightly different formulas for converting color to redshift, but any one of them should be fine. Go to ADS and look for papers with keywords "SDSS photometric redshift", and you should find plenty.

This really shouldn't be too hard. Make a few queries into the SDSS database to gather information on all the companion galaxies which fall into its region, run the resulting colors through a photometric redshift formula, and *voila* you can compare the companion redshifts to the main galaxy redshifts.

Go for it!

Good point StupendousMan! There are actually two different photometric redshifts already calculated in Skyserver. Though since most of the galaxies in your sample are likely z<0.05, their SDSS photozs may not be very reliable (low redshift sources don't have much change in spectral shape across the SDSS filters at low-z).

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"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

Thank you all for the kind words and suggestions! This was an ultimate learning experience.

Having been in a similar situation yourself, I'm sure you can.

I did have a session or two in galaxyzoo, but didn't classify much, somewhere around 100-200 I think. But for this work I looked at thousands of galaxies, and many of them I looked again and again and again... The galaxyzoo newsletter mentioned about the merger project. Might be interesting for us.

I don't know if we have any use for photometric redshifts because I think they're too inaccurate. I have understood that they can be used statistically for very large samples, but when looking at individual objects in a sample of 232 cases, they seem to be too inaccurate for that in my opinion. As an example, I extracted photometric redshifts for 10 objects from SkyServer and compared them to their spectroscopic redshifts. All 10 objects are nearby NGC 450, which is the object that appears when you open SkyServer's navigate-page. Table below gives the object name, spectroscopic redshift, and the two types of photometric redshifts with their errors. One can see that photometric redshifts for this sample of 10 are quite inaccurate, not all of them match the spectrum even if error bars are considered. When we are talking about comparing main galaxy and companion redshifts, they generally have very small differentials, 100 km/s differential in radial velocity (0.0003 in z) might be typical.

We might have a use for photometric redshifts in detecting the grossly discordant redshift "companions" in our sample, though.

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"Stupidity gets denser in a crowd" - Old Finnish saying. [My website] [Nimblebrain forums]

Yes, that sounds like the best use for them. If you can reduce your sample of 232 cases to one of 100 cases, that saves you a lot of time doing spectroscopy ....

Dave and Ari turned a light-weight project into a real research program with paper(s) to ensue. Data collection was a grind but that's OK , since it's done. Analysis and expression may not be so time-consuming. We have a new team member and we're going to flog him to the finish line.

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The ether of general relativity therefore differs from that of classical mechanics or the special theory of relativity respectively, in so far as it is not 'absolute', but is determined in its locally variable properties by ponderable matter.

Albert Einstein, "On the Ether", 1924

Ari and Skip deserve a tremendous amount of credit for keeping the project moving forward as my contributions were often slowed by the ridiculously busy schedule I keep.

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"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

How did I miss this thread. Dave, Skip, Ari, great job. Congratulations.

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Some try to tell me, thoughts they cannot defend,... - Moody Blues.

I'll second that. Nice work guys. pete

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A third rate theory forbids
A second rate theory explains after the fact
A first rate theory predicts...A. Lomonosov