Dynamically close galaxy pairs and merger rate evolution in the CNOC2 redshift survey

We investigate redshift evolution in the galaxy merger and accretion rates, using a well-defined sample of 4184 galaxies with 0.12 less than or equal toz 0.55 and R-C less than or equal to 21.5. We identify 88 galaxies in close (5 less than or equal to r(p) less than or equal to 20 h(-1) kpc) dynamical (Deltav less than or equal to 1500 km s(-1)) pairs. These galaxies are used to compute global pair statistics, after accounting for selection effects resulting from the flux limit, k-corrections, luminosity evolution, and spectroscopic incompleteness. We find that the number of companions per galaxy (for -21 less than or equal to M-B(k,e) less than or equal to -18) is N-c = 0.0321 +/- 0.0077 at z = 0.3. The luminosity in companions, per galaxy, is L-c = 0.0294 +/- 0.0084 x 10(10) h(2) L-circle dot. We assume that is proportional to the galaxy merger rate, while L-c is directly related to the mass accretion rate. After increasing the maximum pair separation to 50 h(-1) kpc and comparing with the low-redshift SSRS2 pair sample, we infer evolution in the galaxy merger and accretion rates of (1+z)(2.3+/-0.7) and (1+z)(2.3+/-0.9), respectively. These are the first such estimates to be made using only confirmed dynamical pairs. When combined with several additional assumptions, this implies that approximately 15% of present epoch galaxies with -21 less than or equal to M-B less than or equal to -18 have undergone a major merger since z = 1.