The Lyman Alpha Reference Sample XV. Relating Ionised Gas Kinematics with Lyman-α observables

Gas kinematics affect the radiative transfer and escape of hydrogen Lyman-α (Lyα) emission from galaxies. We investigate this interplay empirically by relating the ionised gas kinematics of 42 galaxies in the extended Lyα Reference Sample with their Lyα escape fractions, fₑsc, Lyα equivalent widths, EWLyα, and Lyα luminosities, LLyα. To this aim we use PMAS integral-field spectroscopic observations of the Balmer-α line. We calculate shearing velocities, vₛhear, and intrinsic velocity dispersions, σ₀ᵒbs (empirically corrected for beam-smearing effects), as global kinematical measures for each galaxy. The sample is characterised by highly turbulent motions and more than half of the sample shows dispersion dominated kinematics. We uncover clear trends between Lyα observables and global kinematical statistics. We discuss statistically the importance of vₛhear, σ₀ᵒbs, and vₛhear/σ₀ᵒbs for regulating the Lyα observables in comparison to other galaxy parameters. It emerges that σ₀ᵒbs is the dominating parameter for EWLyα and that is as important as nebular extinction, gas covering fraction, and ionising photon production efficiency in regulating fₑsc. A simple scenario where the starburst age is simultaneously regulating turbulence, EWLyα, and fₑsc does not find support by our observations. However, we show that the small scale distribution of dust appears to be influenced by turbulence in some galaxies. In support of our observational result we discuss how turbulence is theoretically expected to play a significant role in modulating fₑsc. (abridged)