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