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Congrats to Turbo on A Catalogue of M51 type Galaxy Associations

  1. May 15, 2008 #1


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    Congrats to Turbo on "A Catalogue of M51 type Galaxy Associations"

    Turbo writes:
    It has been a bit over two years now, but our paper has been accepted at Astrophysics and Space Sciences (a peer-reviewed journal published by Springer) and the preprint is on arXiv.



    The background to this story is kind of interesting. Turbo is actually the name of a pet ferret that Skip Orr had, but I know him by that handle.
    Several years back, Turbo noticed an odd thing about clusters or associations of galaxies. The smaller galaxies in the association seemed to have higher-than-average redshift. It is not clear if this was a just a mirage caused by some artificial skewing of the data that somehow crept in, or whether it was real. So the way to check that was to do a more careful survey and see if it held up.

    they carried it out and produced some solid work, now accepted for publication by Astrophysics and Space Science

    I gather that the original issue that got Turbo started on this is not settled (correct me if I am wrong) but what happened is what often happens in science.
    By doing a careful survey, and assembling a bunch of data where before there were gaps which they filled in, they raised several new questions about this class of galaxies.
    So there is a kind of seredipity operating.

    That is my take on it, more or less off the cuff and at first sight. It would be interesting to hear what Turbo has to say at this point about the survey and the catalogue.

    Turbo (turbo-1) is a long-time PFer.
    His profile https://www.physicsforums.com/member.php?u=9551 says "amateur astronomer"
    Chances are you've already met him in the various PF forums.
    Last edited: May 15, 2008
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  3. May 15, 2008 #2


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    Thank you Marcus. A moderator on another forum asked if anybody had done a study on redshift differentials and if I could prove that smaller galaxies were statistically likely to have higher redshifts than their large host galaxies. To minimize the possibility of contamination from chance projections, I decided to study M51-type galaxy associations. I mined the Arp and Arp-Madore catalogs and presented tentative results showing that companions were far more likely to be redshifted than blueshifted and that the magnitudes of any blueshifts were well within the range of velocities that we might expect to arise from peculiar motion. In contrast, some of the redshifts of companions (even companions with strong secondary evidence for interaction such as tidal streamers, enhanced star formation in the spiral arm, etc) were far too large to permit interaction IF redshift arises only from the Hubble relationship and peculiar motion. Almost immediately, a researcher from Finland jumped in to help extend the sample, as did another well-published researcher from NY state. After two years of work (much of it grinding, since we didn't have grad students to enslave), the catalog is ready to be published.

    The data tables (large!) and the annotated images of all the galaxies are on:

    If you scan the tables, you will see that there has been very little spectroscopy done on the small companions, and I would like to ask that anybody who can help fill this gap do so. These interacting galaxies can be a valuable tool for the study of (triggered) star formation, galaxy morphology and dynamics among other things.
  4. May 15, 2008 #3


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    Indeed Turbo-1 congratulations, but what about the dwarf galaxies associated with the Milky Way, i.e. the LMC and the SMC and large orbiting globular clusters?

    Do they show red-shift?

  5. May 15, 2008 #4


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    Garth, we confined ourselves to M51-type galaxy associations in apparent interaction with one another. Observing redshifts of dwarfs, irregulars, globulars, etc, that did not fit our criteria was outside the scope of the study. We specifically chose M51-type interactions because the morphology of the spiral arms, apparent tidal effects, enhanced star formation, and other secondary indicators of interaction can support the argument that the members are interacting, even if their redshifts may not be concordant.

    We set some fairly stringent conditions on the observations required to accept the associations into the M51 sample, and even then, it took us over 2 years to assemble the catalog, compile the data tables, and refine the paper. If we had tried to extend this study to globulars, dwarf irregulars surrounding nearby large galaxies, etc, we would have needed a huge team and perhaps decades of time.
  6. May 15, 2008 #5


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    I have already pmed turbo earlier, but it won't hurt to repeat it here - congratulations!

    It is nice to see that you still can do something valuable and worth publication without wheelbarrow of cash, just investing your time, brain and patience :)
  7. May 15, 2008 #6


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    Thanks again, Borek! The imaging and information is out there in the public domain, so anybody can undertake a similar research project if they are willing to spend the hours and effort to pull the information together and make sense of it. The NED database, HyperLeda, IRSA, SDSS, etc, etc, are huge troves of data - you don't have to have observing time on a big scope to contribute.

    To those who have access to observing time on big scopes: Very few of the companion galaxies in our sample have published redshifts. If you could manage to help reduce these short-falls, we would welcome your participation!
  8. May 15, 2008 #7
    Did you cross correlate with the SDSS or 2dFGRS for redshifts?
  9. May 15, 2008 #8


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    Our primary redshift sources were NED and HyperLeda. We used other sources as well, including SDSS. Generally, the NED and HyperLeda redshifts are well-annotated so we could assess them by source and date. Sometimes, redshift data are contradictory or at least inconsistent, and we attempted to note conflicts in our data files.
  10. May 16, 2008 #9


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    Congratulations on getting published, skip!
  11. May 20, 2008 #10
    Hi, congrats on the publication!

    It is farly easy to show that the gravitational time dilation at the surface of an (ideal spherical) body is a density type function of mass/(surface radius) rather than a pure function of mass. For example a body with twice the mass and twice the radius of a smaller body would have exactly the same surface gravitational time dilation (or redshift of emmited radiation from the surface) as the smaller body.

    If the smaller body has the same mass M as the larger body, while having a radius n times smaller than the radius R of the larger body, it will have [tex] \sqrt{(Rc^2-2GM)}/\sqrt{(Rc^2-2GMn)}[/tex] greater redshift of its surface radiation than the larger body. Is there any evidence that this is happening? For example, is there any data to suggest the mass to radius ratios of the bodies?

    Appologies, if I am way off the mark ;)
  12. May 20, 2008 #11


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    Thanks, kev. I will have to refrain from answering your question at this time, but I encourage you to mine our data-tables to see if you recognize trends that support your speculation.

    As yet, we have not properly analyzed our data-tables (at least not the the level of rigor that we will hold ourselves to) apart from general trends. We will likely present the trends in our next paper without speculating on the mechanisms behind them, except in general terms. As you can see from the paper and the supporting tables, we not only have some interesting trends in spectroscopy, but also in galaxy morphology, and these trends might eventually be important to our understanding of how galactic interactions can bear on galaxy morphology, galaxy formation, star formation, etc. The frustrating part is that fewer than 20% of the companion galaxies in our sample have published redshifts and that incompleteness will be difficult to rectify without access to large instruments.
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