Pair Analysis of Field Galaxies from the Red-Sequence Cluster Survey

TL;DR

This study analyzes the evolution of galaxy pair counts using a large, volume-limited sample from the RCS-1 survey, revealing how pair fractions change with redshift, luminosity, and separation, and estimating merger rates.

Contribution

It provides the largest dataset for galaxy pair evolution analysis, quantifies the redshift dependence of pair counts, and examines luminosity and separation effects on merger rates.

Findings

Pair count evolution follows (1+z)^m with m=2.83±0.33

Brighter galaxies have smaller m values indicating less evolution

Approximately 6% of galaxies have undergone major mergers since z=0.8

Abstract

We study the evolution of the number of close companions of similar luminosities per galaxy (Nc) by choosing a volume-limited subset of the photometric redshift catalog from the Red-Sequence Cluster Survey (RCS-1). The sample contains over 157,000 objects with a moderate redshift range of 0.25 < z < 0.8 and absolute magnitude in Rc (M_Rc) < -20. This is the largest sample used for pair evolution analysis, providing data over 9 redshift bins with about 17,500 galaxies in each. After applying incompleteness and projection corrections, Nc shows a clear evolution with redshift. The Nc value for the whole sample grows with redshift as (1+z)^m, where m = 2.83 +/- 0.33 in good agreement with N-body simulations in a LCDM cosmology. We also separate the sample into two different absolute magnitude bins: -25 < M_Rc < -21 and -21 < M_Rc < -20, and find that the brighter the absolute magnitude, the smaller the m value. Furthermore, we study the evolution of the pair fraction for different projected separation bins and different luminosities. We find that the m value becomes smaller for larger separation, and the pair fraction for the fainter luminosity bin has stronger evolution. We derive the major merger remnant fraction f_rem = 0.06, which implies that about 6% of galaxies with -25 < M_Rc < -20 have undergone major mergers since z = 0.8.