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<=z<=0.55 and R_C<=21.5. We identify 88 galaxies in close (5<=r_p<=20 h^-1 kpc) dynamical (Δv<=500 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<=M^k,e_B<=-18) is N_c=0.0321+/-0.0077 at z=0.3. The luminosity in companions, per galaxy, is L_c=0.0294+/-0.0084×10¹⁰ h² L_solar. We assume that N_c 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<=M_B<=-18 have undergone a major merger since z=1.