Velocity dispersion vs. gas surface density for the G2 (black solid contour) and G3 (dark-red solid contour) simulated galaxies at 0.625 Gyr with an inclination angle of 30° compared to the PHANGS galaxy sample. The contours are mass-weighted and set to include 20%, 50%, and 80% of the data. The density contours of the PHANGS galaxies (Sun et al. 2020) show the distribution of measurements in galaxy disks (blue shaded contours), the centers of barred galaxies (salmon shaded contours), and the centers of unbarred galaxies (brown dashed contours) with a resolution of 90 pc. The red dashed line marks the position of the median values of α _vir for PHANGS galaxies of 3.1 (Sun et al. 2020). We also show the data for M31 (green solid contour) at 120 pc resolution from Sun et al. (2018). We can see that the FIRE-2 spiral galaxies follow the same σ _v –Σ_mol relation as the PHANGS galaxies.