Gas Content and Kinematics in Clumpy, Turbulent Star-forming Disks

TL;DR

This study shows that local galaxies with properties similar to high-redshift star-forming disks have high molecular gas fractions and velocity dispersions, supporting the idea that gas content influences disk turbulence and clumpiness.

Contribution

It provides new molecular gas mass estimates for local analogs of high-z galaxies and links gas fraction to disk kinematics and stability theory.

Findings

Local analogs share high gas fractions with high-z disks.

A linear relation exists between gas fraction and velocity dispersion to rotation ratio.

High gas fractions correlate with increased clumpiness and shorter depletion times.

Abstract

We present molecular gas mass estimates for a sample of 13 local galaxies whose kinematic and star forming properties closely resemble those observed in $z\approx 1.5$ 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\sim$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 $\sigma$/$v_{c}$, 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 the systems with lowest depletion times ($\sim$0.5 Gyr) have the highest ratios of $\sigma$/$v_{c}$ and more pronounced clumps, even at the same high molecular gas fraction.