merger rate

On day five of The Fabulous, a bit of heat broke out about the merger rate, with the van Dokkums and the Conselices arguing for high rates, and the Pattons and Hoggs for low. Basically, you get low rates if you assume all close pairs merge on a dynamical time (the maximal possible assumption), and you get high rates if you assume all high-asymmetry or faintly-tidal-featured galaxy had a merger in the last dynamical time. Which is more believable? Well, since the close pair rate is an absolute upper limit, I have to assume that either tidal features last for a long time, or they are raised by minor mergers. I don't think there are any other options for resolving this discrepancy.

In related news, it came up at coffee that although the galaxy-galaxy merger rate may or may not be expected to be low, the galaxy group-group merger rate has to be high, because halo mergers are frequent. Now that Berlind has a catalog, lets do it.


  1. Morad pointed out that the maximal rate from close pairs is only low for LRGs—it is high for L-star galaxies. Patton gets low rates of mergers from L-star galaxy pairs because he doesn't assume that they all merge on a dynamical time.

  2. David, got back from Marseille and found your blog :-)

    I'll surelly use your idea of a "working day reporting" thru a blog, hope you don't mind.

    Thanks for many of the comments during the conference and for this "summary" here (which I still have to read carefully and not after 11 hours of planes and trains), it will be useful.

    About the merging rates. Personally I like the idea of a physical maximum estimate using the close pair, but as I could understand it was not taken using "one dynamical time" as merging time.

    Anyway, it would be interesting to estimate the kind of signature (such as asymetries or something else) those sure mergers should leave in the remmanents and check in the surveys its agreement. Basically to see where to draw the line.

    Of course in my case, it would be important to check the rate found by Steve (Zepf), in a very nice work 12 years ago and which are yet used against compact groups as gravitationally bound structures, and see if it is really below the expected value.

    Does it make any sense?

    Very nice meeting you! Send you the pictures url as soon as I have them out of the camera.

  3. Any theories developed while under the influence of coffee are highly suspect. Or, in your case, more suspect.

  4. Cris: Pleased you found it! My "summary" is nowhere near complete; in fact it just contains a few things that stuck out as surprising to me. Looking forward to seeing the photos, if they aren't too embarassing! We will compare what we have to Zepf and let you know what we find.