Evolution in the Continuum Morphological Properties of
  Lyman-Alpha-Emitting Galaxies from z=3.1 to z=2.1
  We present a rest-frame ultraviolet morphological analysis of 108 z=2.1 Lyman
Alpha Emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S) and
compare it to a similar sample of 171 LAEs at z=3.1. Using Hubble Space
Telescope (HST) images from the Galaxy Evolution from Morphology and SEDs
survey, Great Observatories Origins Deep Survey, and Hubble Ultradeep Field, we
measure size and photometric component distributions, where photometric
components are defined as distinct clumps of UV-continuum emission. At both
redshifts, the majority of LAEs have observed half-light radii <~ 2 kpc, but
the median half-light radius rises from 1.0 kpc at z=3.1 to 1.4 kpc at z=2.1. A
similar evolution is seen in the sizes of individual rest-UV components, but
there is no evidence for evolution in the number of multi-component systems. In
the z=2.1 sample, we see clear correlations between the size of an LAE and
other physical properties derived from its SED. LAEs are found to be larger for
galaxies with higher stellar mass, star formation rate, and dust obscuration,
but there is no evidence for a trend between equivalent width and half-light
radius at either redshift. The presence of these correlations suggests that a
wide range of objects are being selected by LAE surveys at z~2, including a
significant fraction of objects for which a massive and moderately extended
population of old stars underlies the young starburst giving rise to the Lyman
alpha emission.
