The Lyman alpha reference sample: IV. Morphology at low and high
  redshift
  We measured the sizes and morphological parameters of LARS galaxies in the
continuum, Lya, and Ha images. We studied morphology by using the Gini
coefficient vs M20 and asymmetry vs concentration diagrams. We then simulated
LARS galaxies at z~2 and 5.7, performing the same morphological measurements.
We also investigated the detectability of LARS galaxies in current deep field
observations. The subsample of LAEs within LARS (LARS-LAEs) was stacked to
provide a comparison to stacking studies performed at high redshift. LARS
galaxies have continuum size, stellar mass, and rest-frame absolute magnitude
typical of Lyman break analogues in the local Universe and also similar to
2<z<3 star-forming galaxies and massive LAEs. LARS optical morphology is
consistent with the one of merging systems, and irregular or starburst
galaxies. For the first time we quantify the morphology in Lya images: even if
a variety of intrinsic conditions of the interstellar medium can favour the
escape of Lya photons, LARS-LAEs appear small in the continuum, and their Lya
is compact. LARS galaxies tend to be more extended in Lya than in the
rest-frame UV. It means that Lya photons escape by forming haloes around HII
regions of LARS galaxies. The stack of LARS-LAE Lya images is peaked in the
centre, indicating that the conditions, which make a galaxy an LAE, tend to
produce a concentrated surface brightness profile. On the other hand, the stack
of all LARS galaxies is shallower and more extended. This can be caused by the
variety of dust and HI amount and distribution, which produces a more complex,
patchy, and extended profile, like the one observed for Lyman break galaxies
that can contribute to the stack. We cannot identify a single morphological
property that controls whether a galaxy emits a net positive Lya flux. However,
the LARS-LAEs have continuum properties consistent with merging systems.
