In this paper we compare the molecular gas depletion times and mid-plane hydrostatic pressure in turbulent, star forming disk galaxies to internal properties of these galaxies. For this analysis we use 17 galaxies from the DYNAMO sample of nearby (z ∼ 0.1) turbulent disks. We find a strong correlation, such that galaxies with lower molecular gas depletion time (t dep ) have higher gas velocity dispersion (σ). Within the scatter of our data, our observations are consistent with the prediction that t dep ∝ σ −1 made in theories of feedback regulated star formation. We also show a strong, single power-law correlation between mid-plane pressure (P) and star formation rate surface density (Σ SFR ), which extends for 6 orders of magnitude in pressure. Disk galaxies with lower pressure are found to be roughly in agreement with theoretical predictions. However, in galaxies with high pressure we find P/Σ SFR values that are significantly larger than theoretical predictions. Our observations could be explained with any of the following: (1) the correlation of Σ SFR − P is significantly sub-linear; (2) the momentum injected from star formation feedback (p * /m * ) is not a single, universal value; or (3) alternate sources of pressure support are important in gas rich disk galaxies. Finally using published survey results, we find that our results are consistent with the cosmic evolution of t dep (z) and σ(z). Our interpretation of these results is that the cosmic evolution of t dep may be regulated not just by the supply of gas, but also the internal regulation of star formation via feedback.

In this letter we study the mean sizes of Hα clumps in turbulent disk galaxies relative to kinematics, gas fractions, and Toomre Q. We use ∼ 100 pc resolution HST images, IFU kinematics, and gas fractions of a sample of rare, nearby turbulent disks with properties closely matched to z ∼ 1.5 − 2 main-sequence galaxies (the DYNAMO sample). We find linear correlations of normalized mean clump sizes with both the gas fraction and the velocity dispersion-to-rotation velocity ratio of the host galaxy. We show that these correlations are consistent with predictions derived from a model of instabilities in a self-gravitating disk (the so-called "violent disk instability model"). We also observe, using a two-fluid model for Q, a correlation between the size of clumps and self-gravity driven unstable regions. These results are most consistent with the hypothesis that massive star forming clumps in turbulent disks are the result of instabilities in self-gravitating gas-rich disks, and therefore provide a direct connection between resolved clump sizes and this in situ mechanism.

We present molecular gas mass estimates for a sample of 13 local galaxies whose kinematic and star forming properties closely resemble those observed in z ≈ 1.5 main-sequence galaxies. Plateau de Bure observations of the CO[1-0] emission line and Herschel Space Observatory observations of the dust emission both suggest molecular gas mass fractions of ∼20%. Moreover, dust emission modeling finds T dust <30K, suggesting a cold dust distribution compared to their high infrared luminosity. The gas mass estimates argue that z ∼0.1 DYNAMO galaxies not only share similar kinematic properties with high-z disks, but they are also similarly rich in molecular material. Pairing the gas mass fractions with existing kinematics reveals a linear relationship between f gas and σ/v c , consistent with predictions from stability theory of a self-gravitating disk. It thus follows that high gas velocity dispersions are a natural consequence of large gas fractions. We also find that systems with lowest t dep (∼0.5 Gyr) have the highest ratios of σ/v c and more pronounced clumps, even at the same high molecular gas fraction.

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