2MASS/SDSS Close Major-Merger Galaxy Pairs: Luminosity Functions and Merger Mass Dependence

TL;DR

This study uses 2MASS and SDSS data to analyze close major-merger galaxy pairs, deriving luminosity functions, pair fractions, and merger rates, revealing mass-independent pair fractions below 10^{11} M_sun and decreasing merger rates for more massive galaxies.

Contribution

First comprehensive analysis of major-merger galaxy pairs combining 2MASS and SDSS data to derive luminosity functions and merger rates in the local universe.

Findings

Nearly constant pair fraction across galaxy masses from 10^9 to 10^11.5 M_sun.

Major-merger pairs involve about 1.6% of galaxies below 10^{11} M_sun.

Merger rates decrease for galaxies with masses above 10^{11} M_sun.

Abstract

We select a close "major-merger candidate" galaxy pair sample in order to calculate the K_{s} luminosity function (LF) and pair fraction representative of the merger/interaction component of galaxy evolution in the local universe. The pair sample (projected separation 5 h$^{-1}$ kpc $\leq$ r $\leq$ 20 h$^{-1}$ kpc, $K_{s}$-band magnitude difference $\Delta$$K_{s}$ $\leq$ 1 mag) is selected by combining the Two Micron All Sky Survey (2MASS) with the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5). The resulting data set contains 340 galaxies covering 5800 sq. degrees. A stellar mass function is also translated from the LF. A differential pair fraction displays nearly constant fraction of galaxy pairs as a function of galaxy mass from 10$^{9}$ to 10$^{11.5}$ M$_{\sun}$ . The differential pair fraction is less subject to absolute magnitude bias due to survey limitations than the standard total pair fraction. These results suggest that major-merger candidate pairs in the 0$<$z$<$0.1 universe are developed from $\sim$1.6% of the galaxy population without dependance on galaxy mass for pair components below 10$^{11}$ M$_{\sun}$. The derived LF combined with merger model time scales give local merger rates per unit volume which decrease with masses greater than 10$^{11}$ M$_{\sun}$ .