(Top) SFR history for the G2 and G3 merger with “e2” orbit with a viewing angle of “v0.” The three solid black vertical lines indicate the time for each snapshot displayed below. The two dashed lines indicate the times at the start of the second merging and the final coalescence of two nuclei. (Bottom) Three rows of snapshots of the simulated mergers. For each snapshot, the left panel shows the σ _v vs. Σ_mol mass-weighted contour with the same setting as Figure 1. We also show the density contours for the PHANGS galaxies (blue shaded region), NGC 3256 (blue contours), and the Antennae (orange shaded region). For NGC 3256, Σ_mol is calculated using the ULIRG α _CO of 1.1 ﹩{M}_{\odot }\ {\left({\rm{K}}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{pc}}^{2}\right)}^{-1}﹩. For the Antennae, the gas surface density is calculated using the Milky Way α _CO of 4.3 ﹩{M}_{\odot }\ {\left({\rm{K}}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{pc}}^{2}\right)}^{-1}﹩. The red dashed line indicates the line of constant α _vir of 3.1. The right two panels show the Σ_mol and α _vir maps of the inner 5 kpc regions where we have most of our detected pixels. The interactive version of the animation is available at https://heh15.github.io/merger_animation/G2G3_e2_v0_final and contains the panels of SFR history, σ _v vs. Σ_mol diagram, and Σ_mol map. You can drag the slide to view mergers at different times. The scripts and data to generate the animation are stored in the Zenodo repository doi:10.5281/zenodo.7796593. We can see that the properties of the GMCs right before the second passage still resemble those of normal spiral galaxies, while GMCs after the second passage lie above the PHANGS trend in the σ _v vs. Σ_mol plot and show significantly higher α _vir.

An interactive version of this figure is available in the online journal.