Caltech Faint Galaxy Redshift Survey. XI. The Merger Rate to Redshift 1 from Kinematic Pairs.

Area of Science:

• Cosmic evolution and galaxy formation
• Astrophysical processes governing galaxy mergers

Background:

• Galaxy mergers significantly contribute to mass accumulation.
• Understanding merger rates requires accounting for galaxy mass, density, and velocity.
• Fractional luminosity in kinematic pairs offers a robust merger estimator, insensitive to population evolution.

Purpose of the Study:

• To measure the rate and redshift evolution of galaxy merging.
• To quantify mass accretion via mergers in galaxies.
• To assess the impact of mergers on galaxy mass over cosmic time.

Main Methods:

• Utilized a k-corrected, evolution-compensated sample from Caltech Faint Galaxy Redshift Survey and COSMOS survey.
• Identified kinematic pairs with specific projected separations and velocity differences.
• Modeled fractional luminosity in pairs and derived conversion factors to physical merger rates.

Main Results:

• The mass accretion rate per galaxy (M1,M2>/=0.2M*) is 0.02+/-0.01(1+z)^0.1+/-0.5M* Gyr^-1.
• Present-day high-luminosity galaxies accreted approximately 0.15M* of their mass since redshift 1 (approx. 7 Gyr).
• Merger effects are perturbative for massive galaxies but dramatic for lower-mass galaxies.

Conclusions:

• Galaxy merging is a significant contributor to galaxy mass growth over cosmic time.
• The fractional mass increase due to mergers is substantial for low-mass galaxies.
• Merger evolution is dominated by galaxy correlation and velocity evolution, not density evolution.