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We study the spatially resolved (sub-kpc) gas velocity dispersion($\sigma$)--star formation rate (SFR) relation in the FIRE-2 (Feedback inRealistic Environments) cosmological simulations. We specifically focus onMilky Way mass disk galaxies at late times. In agreement with observations, wefind a relatively flat relationship, with $\sigma \approx 15-30$ km/s inneutral gas across 3 dex in SFRs. We show that higher dense gas fractions(ratios of dense gas to neutral gas) and SFRs are correlated at constant$\sigma$. Similarly, lower gas fractions (ratios of gas to stellar mass) arecorrelated with higher $\sigma$ at constant SFR. The limits of the$\sigma$-$\Sigma_{\rm SFR}$ relation correspond to the onset of strongoutflows. We see evidence of "on-off" cycles of star formation in thesimulations, corresponding to feedback injection timescales of 10-100 Myr,where SFRs oscillate about equilibrium SFR predictions. Finally, SFRs andvelocity dispersions in the simulations agree well with feedback-regulated andmarginally stable gas disk (Toomre's $Q =1$) model predictions, and the dataeffectively rule out models assuming that gas turns into stars at (low)constant efficiency (i.e., ${\rm 1\%}$ per free-fall time). And although thesimulation data do not entirely exclude gas accretion/gravitationally poweredturbulence as a driver of $\sigma$, it appears to be strongly subdominant tostellar feedback in the simulated galaxy disks.

Swirls of FIRE: Spatially Resolved Gas Velocity Dispersions and Star Formation Rates in FIRE-2 Disk Environments