The Σ_mol and σ _v variation across the second passage and final coalescence of the G2 and G3 merger at “e2” orbit with a viewing angle of “v0.” The two dashed vertical lines indicate the times when the simulated merger begins the second passage and experiences final coalescence. The three solid vertical lines correspond to the three snapshots shown in Figure 2. The horizontal dashed lines indicate the median value of the isolated G3 galaxy at a time of 0.625 Gyr (Figure 1) as a baseline for comparison. (Upper left) Σ_mol vs. time. Blue lines show the mass-weighted median Σ_mol of the entire merger, while the orange shaded area indicates the Σ_mol range between the 16th and 84th percentiles. The two dashed lines indicate the time for the start of the second passage and the final coalescence of the two nuclei. (Upper right) Ratio between the median Σ_mol at a given time and the median value Σ_mol,0 for the isolated G3 galaxy at 0.625 Gyr. (Lower left) Mass-weighted median σ _v vs. time. (Lower right) Ratio between the median σ _v and the value σ _v,0 for isolated G3 galaxies at 0.625 Gyr. We can see that both Σ_mol and σ _v increase dramatically during the second passage when the extreme starburst happens.