Cold molecular gas in merger remnants. II.

Sixteen molecular lines from 14 different molecular species and isotopologues were identified, and 21 out of 28 sources were detected in one or more molecular lines. On average, the line ratios of the dense gas tracers, such as HCN(1-0) and HCO^+^(1-0), to ^13^CO(1-0) are 3-4 times higher in ultra/luminous infrared galaxies (U/LIRGs) than in non-LIRGs in our sample.

These high line ratios could be explained by the deficiency of ^13^CO and high dense gas fractions suggested by high HCN(1-0)/^12^CO(1-0) ratios. We calculate the IR-to-HCN(1-0) luminosity ratio as a proxy of the dense gas star formation efficiency. There is no correlation between the IR/HCN ratio and the IR luminosity, while the IR/HCN ratio varies from source to source ((1.1-6.5)x10^3^L_{sun}_/(K.km/s.pc^2^)).