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-alpha (Ly alpha) emission from galaxies. We investigate this interplay empirically by relating the ionised gas kinematics of 42 galaxies in the extended Ly alpha Reference Sample (eLARS) with their Ly alpha escape fractions, f(esc)(Ly alpha), Ly alpha equivalent widths, EWLy alpha, and Ly alpha luminosities, L-Ly alpha. To this aim we use PMAS integral-field spectroscopic observations of the Balmer-alpha line. Our sample contains 18 rotating discs, 13 perturbed rotators, and 13 galaxies with more complex kinematics. The distributions of f(esc)(Ly alpha), EWLy alpha, and L-Ly alpha do not differ significantly between these kinematical classes, but the largest Ly alpha observables are found amongst the kinematically complex systems. We find no trends between either f(esc)(Ly alpha) or EWLy alpha and kinematic or photometric inclinations. We calculate shearing velocities, v(shear), and intrinsic velocity dispersions, sigma(obs)(0) (empirically corrected for beam-smearing effects), as global kinematical measures for each galaxy. The sample is characterised by highly turbulent motions (30 km s(-1) less than or similar to sigma(obs)(0) less than or similar to 80 km s(-1)) and more than half of the sources show dispersion-dominated kinematics. We uncover clear trends between Ly alpha observables and global kinematical statistics: EWLy alpha and L-Ly alpha correlate with sigma(obs)(0), while f(esc)(Ly alpha) anti-correlates with v(shear) and v(shear)/sigma(obs)(0). Moreover, we find, that galaxies with EWLy alpha >= 20 & Aring; are characterised by higher sigma(0) and lower v(shear)/sigma(obs)(0) than galaxies below this threshold. We discuss the statistical importance of v(shear), sigma(obs)(0), and v(shear)/sigma(obs)(0) for regulating the Ly alpha observables in comparison to other galaxy parameters. It emerges that sigma(obs)(0) is the dominating parameter for regulating EWLy alpha and that is as important as nebular extinction, gas covering fraction, and ionising photon production efficiency in regulating f(esc)(Ly alpha). A simple scenario where the starburst age is simultaneously regulating turbulence, EWLy alpha, and f(esc)(esc) is not supported 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 f(esc)(Ly alpha).