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trinitree88
2012-Aug-22, 01:38 PM
Here's a paper that says merger rates of galaxies increase with redshift. :http://iopscience.iop.org/0004-637X/702/2/1005/fulltext/
But the new one says the merger rate should be constant at all redshifts:SEE:http://arxiv.org/abs/1206.2532

So, I'll take a galaxy expert's opinion on what to believe. Thanks. pete

antoniseb
2012-Aug-22, 03:52 PM
I believe I'll wait before I say anything definitive on this topic, but is sure seems to me like the time around z=7 should be one big-fat-constant merger period with lots of dwarf galaxies coming together to make the big ones... but that's hand-waving talk, and actual math and observations can override that any time.

ngc3314
2012-Aug-22, 06:14 PM
I'm a little cynical about both those specific papers with my observer's bias, since they each have such a big dose of theoretical analysis. Observational studies do suggest that the merger rate used to be higher, but vary a good bit on how much it's changed. (Digression warning) These studies count either the fraction of galaxies as functions of luminosity and redshift which show merger signatures - tidal tails, double nuclei - or the fraction of galaxies in close pairs. The pair fraction gives a merger rate because merging happens overwhelmingly within pairs and small groups, for which the relative velocities are close to the circular velocities in each galaxy (an especially favorable situation for the energy transfer that drives merging). Thus, to first order, the merger rate is the time derivative of the galaxy pair fraction. At high redshifts, the Tolman surface-brightness dimming makes tidal tails very difficult to find, so the pair-fraction technique has more traction heading into the early epochs of galaxy history. (I would still say that even if I didn't have a paper applying it back in 1994. Honest.)

trinitree88
2012-Aug-22, 07:12 PM
I'm a little cynical about both those specific papers with my observer's bias, since they each have such a big dose of theoretical analysis. Observational studies do suggest that the merger rate used to be higher, but vary a good bit on how much it's changed. (Digression warning) These studies count either the fraction of galaxies as functions of luminosity and redshift which show merger signatures - tidal tails, double nuclei - or the fraction of galaxies in close pairs. The pair fraction gives a merger rate because merging happens overwhelmingly within pairs and small groups, for which the relative velocities are close to the circular velocities in each galaxy (an especially favorable situation for the energy transfer that drives merging). Thus, to first order, the merger rate is the time derivative of the galaxy pair fraction. At high redshifts, the Tolman surface-brightness dimming makes tidal tails very difficult to find, so the pair-fraction technique has more traction heading into the early epochs of galaxy history. (I would still say that even if I didn't have a paper applying it back in 1994. Honest.)

Thanks NGC. That clarifies it nicely.