The Oxygen Abundances of Luminous and Ultraluminous Infrared Galaxies

Luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) dominate the star formation rate budget of the universe at z ≳ 1, yet no local measurements of their heavy-element abundances exist. We measure nuclear or near-nuclear oxygen abundances in a sample of 100 star-forming LIRGs and ULIRGs using new, previously published, and archival spectroscopy of strong emission lines (including [O II] λλ3726, 3729) in galaxies with redshifts ⟨ z⟩ ∼ 0.1. When compared to local emission-line galaxies of similar luminosity and mass (using the near-infrared luminosity-metallicity and mass-metallicity relations), we find that LIRGs and ULIRGs are underabundant by a factor of 2 on average. As a corollary, LIRGs and ULIRGs also have smaller effective yields. We conclude that the observed underabundance results from the combination of a decrease of abundance with increasing radius in the progenitor galaxies and strong, interaction- or merger-induced gas inflow into the galaxy nucleus. This conclusion demonstrates that local abundance scaling relations are not universal, a fact that must be accounted for when interpreting abundances earlier in the universe's history, when merger-induced star formation was the dominant mode. We use our local sample to compare to high-redshift samples and assess abundance evolution in LIRGs and ULIRGs. We find that abundances in these systems increased by ~0.2 dex from z ∼ 0.6 to z ∼ 0.1. Evolution from z ∼ 2 submillimeter galaxies to z ∼ 0.1 ULIRGs also appears to be present, although uncertainty due to spectroscopic limitations is large.