The Lyman alpha reference sample. VII. Spatially resolved H$\alpha$ 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 $\alpha$ (H$\alpha$) emission in our data cubes. These maps trace the spectral and spatial properties of the LARS galaxies' intrinsic Ly$\alpha$ radiation field. We show our kinematic maps spatially registered onto the Hubble Space Telescope H$\alpha$ and Lyman $\alpha$ (Ly$\alpha$) images. Only for individual galaxies a causal connection between spatially resolved H$\alpha$ kinematics and Ly$\alpha$ 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 ${\sigma }_0$, shearing velocity $v_{\mathrm{shear}}$, and the $v_{\mathrm{shear}}/{\sigma }_0$ 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). $v_{\mathrm{shear}}/{\sigma }_0$ 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 $v_{\mathrm{shear}}/{\sigma }_0<1$ and are thus kinematically similar to turbulent star forming galaxies seen at high redshift. When linking our kinematical statistics to the global LARS Ly$\alpha$ properties, we find that dispersion dominated systems show higher Ly$\alpha$ equivalent widths and higher Ly$\alpha$ escape fractions than systems with $v_{\mathrm{shear}}/{\sigma }_0>1$. Our result indicates that turbulence in actively star-forming systems is causally connected to interstellar medium conditions that favour an escape of Ly$\alpha$ radiation.

26 pages, 15 figures, accepted for publication in A&A

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