Galaxy pairs in the Sloan Digital Sky Survey – VII. The merger–luminous infrared galaxy connection

We use a sample of 9397 low-redshift (z ≤ 0. 1) galaxies with a close companion to investigate the connection between mergers and luminous infrared (IR) galaxies (LIRGs). The pairs are selected from the Sloan Digital Sky Survey (SDSS) and have projected separations rp ≤ 80 h|^{- 1₇₀}| kpc, relative velocities ΔV ≤ 300 km s−1 and stellar mass ratios within a factor of 1: 10. A control sample consisting of four galaxies per pair galaxy is constructed by simultaneously matching in stellar mass, redshift and environment to galaxies with no close companion. The IR luminosities (LIR) of galaxies in the pair and control samples are determined from the SDSS – Infrared Astronomical Satellite (IRAS) matched catalogue of Hwang et al. Over the redshift range of our pairs sample, the IRAS matches are complete to LIRG luminosities (LIR ≥ 1011 L⊙), allowing us to investigate the connection between mergers and luminous IR galaxies. We find a trend for increasing LIRG fraction towards smaller pair separations, peaking at a factor of ∼5–10 above the median control fraction at the smallest separations (rp 10. 5), likely because the SFR enhancement required to produce LIRG luminosities is more modest than at low masses. The ΔSFR offers a redshift-independent metric for the identification of the galaxies with the most enhanced star-forming rates that does not rely on fixed LIR boundaries.