The Merger Rate to Redshift One from Kinematic Pairs: Caltech Faint Galaxy Redshift Survey XI

TL;DR

This study measures galaxy merger rates up to redshift one using kinematic pairs from the Caltech Faint Galaxy Redshift Survey, revealing a modest increase in merger activity with redshift and quantifying mass accretion over cosmic time.

Contribution

It introduces a method to estimate galaxy merger rates from kinematic pair data, accounting for population evolution and converting redshift space statistics to physical merger rates.

Findings

Merger rate per galaxy is approximately 0.02 M* Gyr^{-1} at z=0.

Galaxies have accreted about 0.15 M* of mass since redshift one.

Merger activity shows a mild increase with redshift, with m_L around 0.6.

Abstract

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 which is relatively insensitive to population evolution. Here we use a k-corrected and evolution compensated volume-limited sample drawing about 300 redshifts from CFGRS and 3000 from CNOC2 to measure the rate and redshift evolution of merging. We identify kinematic pairs with projected separations less than either 50 or 100 \hkpc and rest-frame velocity differences of less than 1000\kms. The fractional luminosity in pairs is modeled as f_L(Delta v,r_p,M_r^{ke})(1+z)^{m_L} 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<= 50 and 100\hkpc, respectively (Omega_M=0.2, Omega_Lambda=0.8). The value of m_L 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 physical space pair density, a merger probability and a mean in-spiral time. The resulting mass accretion rate per galaxy (M_1,M_2>= 0.2 M*) is 0.02+/-0.01(1+z)^{0.1+/-0.5} M*~Gyr^{-1}. Present day high-luminosity galaxies therefore have accreted approximately 0.15M* of their mass over the approximately 7 Gyr to redshift one. (abridged)