Extreme gas fractions in clumpy, turbulent disk galaxies at z~0.1

TL;DR

This study discovers high gas fractions and turbulent disk dynamics in nearby galaxies, resembling high-redshift galaxies, providing insights into galaxy evolution and the link between gas content and star formation.

Contribution

It demonstrates that local galaxies can serve as analogues for high-redshift turbulent disks, revealing high gas fractions and dynamic states similar to those in early universe galaxies.

Findings

Gas fractions of 20-30% in local galaxies

High dispersion rotating disks similar to high-z galaxies

Depletion times around 0.5 Gyr

Abstract

In this letter we report the discovery of CO fluxes, suggesting very high gas fractions in three disk galaxies seen in the nearby Universe (z ~ 0.1). These galaxies were investigated as part of the DYnamics of Newly Assembled Massive Objects (DYNAMO) survey. High-resolution Hubble Space Telescope imaging of these objects reveals the presence of large star forming clumps in the bodies of the galaxies, while spatially resolved spectroscopy of redshifted Halpha reveals the presence of high dispersion rotating disks. The internal dynamical state of these galaxies resembles that of disk systems seen at much higher redshifts (1 < z < 3). Using CO(1-0) observations made with the Plateau de Bure Interferometer, we find gas fractions of 20-30% and depletion times of tdep ~ 0.5 Gyr (assuming a Milky Way-like CO conversion factor). These properties are unlike those expected for low- redshift galaxies of comparable specific star formation rate, but they are normal for their high-z counterparts. DYNAMO galaxies break the degeneracy between gas fraction and redshift, and we show that the depletion time per specific star formation rate for galaxies is closely tied to gas fraction, independent of redshift. We also show that the gas dynamics of two of our local targets corresponds to those expected from unstable disks, again resembling the dynamics of high-z disks. These results provide evidence that DYNAMO galaxies are local analogues to the clumpy, turbulent disks, which are often found at high redshift.