The Lyman Alpha Reference Sample: V. The impact of neutral ISM
  kinematics and geometry on Lyman Alpha escape
  We present high-resolution far-UV spectroscopy of the 14 galaxies of the
Lyman Alpha Reference Sample; a sample of strongly star-forming galaxies at low
redshifts ($0.028 < z < 0.18$). We compare the derived properties to global
properties derived from multi band imaging and 21 cm HI interferometry and
single dish observations, as well as archival optical SDSS spectra. Besides the
Lyman $\alpha$ line, the spectra contain a number of metal absorption features
allowing us to probe the kinematics of the neutral ISM and evaluate the optical
depth and and covering fraction of the neutral medium as a function of
line-of-sight velocity. Furthermore, we show how this, in combination with
precise determination of systemic velocity and good Ly$\alpha$ spectra, can be
used to distinguish a model in which separate clumps together fully cover the
background source, from the "picket fence" model named by Heckman et al.
(2011). We find that no one single effect dominates in governing Ly$\alpha$
radiative transfer and escape. Ly$\alpha$ escape in our sample coincides with a
maximum velocity-binned covering fraction of $\lesssim 0.9$ and bulk outflow
velocities of $\gtrsim 50$ km s$^{-1}$, although a number of galaxies show
these characteristics and yet little or no Ly$\alpha$ escape. We find that
Ly$\alpha$ peak velocities, where available, are not consistent with a strong
backscattered component, but rather with a simpler model of an intrinsic
emission line overlaid by a blueshifted absorption profile from the outflowing
wind. Finally, we find a strong anticorrelation between H$\alpha$ equivalent
width and maximum velocity-binned covering factor, and propose a heuristic
explanatory model.
