Ratio between the molecular gas mass within the central 1 kpc radius circle of the G3 galaxy and the total molecular gas inside our FOV of 25 kpc. During the second coalescence between 2.7 and 3.2 Gyr, more than 50% of the molecular gas is concentrated within the central 1 kpc region, which indicates that the Σ_mol increase we see in the simulated merger during the second passage is probably due to this gas concentration.