The SAMI Galaxy Survey: Gas velocity dispersions in low-$z$ star-forming galaxies and the drivers of turbulence

Abstract

We infer the intrinsic ionised gas kinematics for 383 star-forming galaxies across a range of integrated star-formation rates (SFR $\in [10^{-3},10^2]$ M${}_{\odot }$ yr${}^{-1}$) at $z\lesssim 0.1$ using a consistent 3D forward-modelling technique. The total sample is a combination of galaxies from the SAMI Galaxy Survey and DYNAMO survey. For typical low-$z$ galaxies taken from the SAMI Galaxy Survey, we find the vertical velocity dispersion ($\ddot{I}{ƒ}_{v,z}$) to be positively correlated with measures of star-formation rate, stellar mass, HI gas mass, and rotational velocity. The greatest correlation is with star-formation rate surface density ($\hat{I}{\pounds }_{\text{SFR}}$). Using the total sample, we find $\ddot{I}{ƒ}_{v,z}$ increases slowly as a function of integrated star-formation rate in the range SFR $\in$ [$10^{-3}$, 1] M${}_{\odot }$ yr${}^{-1}$ from $17\pm 3$ km s${}^{-1}$ to $24\pm 5$ km s${}^{-1}$ followed by a steeper increase up to $\ddot{I}{ƒ}_{v,z}$ $\sim 80$ km s${}^{-1}$ for SFR $\gtrsim 1$ M${}_{\odot }$ yr${}^{-1}$. This is consistent with recent theoretical models that suggest a $\ddot{I}{ƒ}_{v,z}$ floor driven by star-formation feedback processes with an upturn in $\ddot{I}{ƒ}_{v,z}$ at higher SFR driven by gravitational transport of gas through the disc.

27 pages, 10 figures, accepted for MNRAS