2010MNRAS.406.1364L

Luminous infrared galaxies (L_IR> 10¹¹L_☉) are often associated with interacting galactic systems and are thought to be powered by merger-induced starbursts and/or dust-enshrouded active galactic nucleus. In such systems, the evolution of the dense, star-forming molecular gas as a function of merger separation is of particular interest. Here, we present observations of the CO(3-2) emission from a sample of luminous infrared galaxy mergers that span a range of galaxy-galaxy separations. The excitation of the molecular gas is studied by examining the CO(3-2)/CO(1-0) line ratio, r₃₁, as a function of merger extent. We find these line ratios, r₃₁, to be consistent with kinetic temperatures of T_k= (30-50)K and gas densities of. We also find weak correlations between r₃₁ and both merger progression and star formation efficiency [L_FIR/L_CO(1–0)]. These correlations show a tendency for gas excitation to increase as the merger progresses and the star formation efficiency rises. To conclude, we calculate the contributions of the CO(3-2) line to the 850-µm fluxes measured with SCUBA (Submillimetre Common-User Bolometer Array), which are seen to be significant (∼22 per cent).