The SAMI Galaxy Survey: gas content and interaction as the drivers of kinematic asymmetry

In order to determine the causes of kinematic asymmetryin the H$\ alpha$ gas in the SAMI Galaxy Survey sample, we investigate the comparative influences of environment and intrinsic properties of galaxieson perturbation. We use spatially resolved H$\ alpha$ velocity fields from the SAMI GalaxySurvey to quantify kinematic asymmetry($\ overline{v_{asym}}$) in nearby galaxiesand environmental and stellar mass data from the GAMA survey. {We find that local environment, measured as distance to nearest neighbour, is inversely correlated with kinematic asymmetryfor galaxieswith $\mathrm{\log(M_*/M_\odot)}>10.0$, but there is no significant correlation for galaxieswith $\mathrm{\log(M_*/M_\odot)}<10.0$. Moreover, low mass galaxies($\mathrm{\log(M_*/M_\odot)}<9.0$) have greater kinematic asymmetryat all separations, suggesting a different physical source of asymmetryis important in low mass galaxies.} We propose that secular effects derived from gas fraction and gas mass may be the primary causes of asymmetryin low mass galaxies. High gas fraction is linked to high $\frac{\sigma_{m}}{V}$ (where $\sigma_m$ is H$\ alpha$ velocity dispersion and $V$ the rotation velocity), which is strongly correlated with $\ overline{v_{asym}}$, and galaxieswith $\log(M_*/M_\odot)<9.0$ have offset $\ overline{\frac{\sigma_{m}}{V}}$ from the rest of the sample. Further, asymmetryas a fraction of dispersion decreases for galaxieswith $\log(M_*/M_\odot)<9.0$. Gas mass and asymmetryare also inversely correlated in our sample. We propose that low gas masses in dwarf galaxiesmay lead to asymmetric distribution of gas clouds, leading to increased relative turbulence.