Evolution of the Frequency of Luminous (\geq L_V*) Close Galaxy Pairs at z < 1.2 in the COSMOS Field

TL;DR

This study measures how the fraction of luminous galaxy pairs changes up to redshift 1.2, revealing a strong evolution that suggests mergers play a key role in galaxy evolution during z=1 to 3.

Contribution

It provides the first comprehensive measurement of luminous galaxy pair fraction evolution up to z=1.2 using COSMOS data, indicating a power-law increase with redshift.

Findings

Pair fraction evolves as (1+z)^{3.1}

Approximately 50% of luminous galaxies at z~2 are in close pairs

Galaxy mergers are likely dominant in galaxy evolution at z=1-3

Abstract

We measure the fraction of luminous galaxies in pairs at projected separations of 5-20 kpc out to z=1.2 in the COSMOS field using ACS images and photometric redshifts derived from an extensive multiwavelength dataset. Analysis of a complete sample of 106,188 galaxies more luminous than M_V=-19.8 (~ L_V*) in the redshift range 0.1 < z < 1.2 yields 1,749 galaxy pairs. These data are supplemented by a local z=0-0.1 value for the galaxy pair fraction derived from the Sloan Digital Sky Survey (SDSS). After statistically correcting the COSMOS pair sample for chance line-of-sight superpositions, the evolution in the pair fraction is fit by a power law \propto (1+z)^{n=3.1 \pm 0.1}. If this strongly evolving pair fraction continues out to higher redshift, ~ 50% of all luminous galaxies at z ~ 2 are in close pairs. This clearly signifies that galaxy mergers are a very significant and possibly dominant mechanism for galaxy evolution during the epoch of galaxy formation at z=1 to 3.