The Stability of Galaxy Disks
  We calculate the stellar surface mass density (Sigma_*) and two-component
(gas+stars) disk stability (Q_RW) for 25 late-type galaxies from the DiskMass
Survey. These calculations are based on fits of a dynamical model to our
ionized-gas and stellar kinematic data performed using a Markov Chain Monte
Carlo sampling of the Bayesian posterior. Marginalizing over all galaxies, we
find a median value of Q_RW=2.0+/-0.9 at 1.5 scale lengths. We also find that
Q_RW is anti-correlated with the star-formation rate surface density
(Sigma_SFR), which can be predicted using a closed set of empirical scaling
relations. Finally, we find that the star-formation efficiency
(Sigma_SFR/Sigma_g) is correlated with Sigma_* and weakly anti-correlated with
Q_RW. The former is consistent with an equilibrium prediction of
Sigma_SFR/Sigma_g propto Sigma_*^{1/2}. Despite its order-of-magnitude range,
we find no correlation of Sigma_SFR/Sigma_g/Sigma_*^{1/2} with any other
physical quantity derived by our study.
