The diskmass survey. VIII. On the relationship between disk stability and star formation

We study the relationship between the stability level of late-type galaxy disks and their star-formation activity using integral-field gaseous and stellar kinematic data. Specifically, we compare the two-component (gas+stars) stability parameter from Romeo and Wiegert (Q _RW), incorporating stellar kinematic data for the first time, and the star-formation rate estimated from 21 cm continuum emission. We determine the stability level of each disk probabilistically using a Bayesian analysis of our data and a simple dynamical model. Our method incorporates the shape of the stellar velocity ellipsoid (SVE) and yields robust SVE measurements for over 90% of our sample. Averaging over this subsample, we find a meridional shape of σ_z/σ_R=0.51_−0.25^+0.36 for the SVE and, at 1.5 disk scale lengths, a stability parameter of Q _RW = 2.0 ± 0.9. We also find that the disk-averaged star-formation-rate surface density ( Σ-dot _e,∗) is correlated with the disk-averaged gas and stellar mass surface densities (Σ _{e, g} and Σ _{e, *}) and anti-correlated with Q _RW. We show that an anti-correlation between Σ-dot _e,∗ and Q _RW can be predicted using empirical scaling relations, such that this outcome is consistent with well-established statistical properties of star-forming galaxies. Interestingly, Σ-dot _e,∗ is not correlated with the gas-only or star-only Toomre parameters, demonstrating the merit of calculating a multi-component stability parameter when comparing to star-formation activity. Finally, our results are consistent with the Ostriker et al. model of self-regulated star-formation, which predicts Σ-dot _e,∗/Σ_e,g∝Σ_e,∗^1/2. Based on this and other theoretical expectations, we discuss the possibility of a physical link between disk stability level and star-formation rate in light of our empirical results.