Merger rates at z~3

from Bluck et al., http://arxiv.org/pdf/0812.0926

The authors use pair counts and galaxy morphologies (CAS) to estimate
merger rates in the GOODS North and South fields. The plot above
shows the merger fraction for galaxies above log(M)=11. At z>3 the
merger rate continues to increase, so the peak of merger activity for
these galaxies must be at higher redshifts. This is in contrast to
lower-mass galaxies (10^10), where the merger peak is seen around
z=2. Thus, the authors conclude that high-mass galaxies undergo
major mergers at higher redshifts than lower-mass galaxies.