Caltech Faint Galaxy Redshift Survey. XI. The merger rate to redshift 1 from kinematic pairs

The rate of mass accumulation due to galaxy merging depends on the mass, density, and velocity distribution of galaxies in the near neighborhood of a host galaxy. The fractional luminosity in kinematic pairs combines all of these effects in a single estimator that is relatively insensitive to population evolution. Here we use a k-corrected and evolution-compensated volume-limited sample having an R-band absolute magnitude of M-R(k,e) less than or equal to -19.8 + 5 log h mag drawing about 300 redshifts from the Caltech Faint Galaxy Redshift Survey and 3000 from the Canadian Network for Observational Cosmology field galaxy survey to measure the rate and redshift evolution of merging. The combined sample has an approximately constant comoving number and luminosity density from redshift 0.1 to 1.1 (Omega(M) = 0.2, Omega(Lambda) = 0.8); hence, any merger evolution will be dominated by correlation and velocity evolution, not density evolution. We identify kinematic pairs with projected separations less than either 50 or 100 h(-1) kpc and rest-frame velocity differences of less than 1000 km s(-1). The fractional luminosity in pairs is modeled as f(L)(Delta upsilon, r(p), M-r(k,e))(1 + z)(mL), where [f(L), m(L)] are [0.14 +/- 0.07, 0 +/- 1.4] and [0.37 +/- 0.7, 0.1 +/- 0.5] for r(p) less than or equal to 50 and 100 h(-1) kpc, respectively (Omega(M) = 0.2, Omega(Lambda) = 0.8). The value of rn, is about 0.6 larger if Lambda = 0. To convert these redshift-space statistics to a merger rate, we use the data to derive a conversion factor to a physical space pair density, a merger probability, and a mean in-spiral time. The resulting mass accretion rate per galaxy (M-1, M-2 greater than or equal to 0.2M*) is 0.02 +/- 0.01(1 + z)M0.1+/-0.5*. Gyr(-1). Present-day high-luminosity galaxies therefore have accreted approximately 0.15M* of their mass over the approximately 7 Gyr to redshift 1. Since merging is likely only weakly dependent on the host mass, the fractional effect, delta M/M similar or equal to 0.15M*/M, is dramatic for lower mass galaxies but is, on the average, effectively perturbative for galaxies above 1M*.