The Lyman alpha reference sample. VII. Spatially resolved H$α$ kinematics

Abstract

We present integral field spectroscopic observations with the Potsdam Multi Aperture Spectrophotometer of all 14 galaxies in the $z\sim 0.1$ Lyman Alpha Reference Sample (LARS). We produce 2D line of sight velocity maps and velocity dispersion maps from the Balmer $α$ (H$α$) emission in our data cubes. These maps trace the spectral and spatial properties of the LARS galaxies' intrinsic Ly$α$ radiation field. We show our kinematic maps spatially registered onto the Hubble Space Telescope H$α$ and Lyman $α$ (Ly$α$) images. Only for individual galaxies a causal connection between spatially resolved H$α$ kinematics and Ly$α$ photometry can be conjectured. However, no general trend can be established for the whole sample. Furthermore, we compute non-parametric global kinematical statistics -- intrinsic velocity dispersion $σ_0$, shearing velocity $v_\mathrm{shear}$, and the $v_\mathrm{shear}/σ_0$ ratio -- from our kinematic maps. In general LARS galaxies are characterised by high intrinsic velocity dispersions (54\,km\,s$^{-1}$ median) and low shearing velocities (65\,km\,s$^{-1}$ median). $v_\mathrm{shear}/σ_0$ values range from 0.5 to 3.2 with an average of 1.5. Noteworthy, five galaxies of the sample are dispersion dominated systems with $v_\mathrm{shear}/σ_0 <1$ and are thus kinematically similar to turbulent star forming galaxies seen at high redshift. When linking our kinematical statistics to the global LARS Ly$α$ properties, we find that dispersion dominated systems show higher Ly$α$ equivalent widths and higher Ly$α$ escape fractions than systems with $v_\mathrm{shear}/σ_0 > 1$. Our result indicates that turbulence in actively star-forming systems is causally connected to interstellar medium conditions that favour an escape of Ly$α$ radiation.