Non-parametric analysis of the rest-frame UV sizes and morphological
  disturbance amongst L* galaxies at 4<z<8
  We present the results of a study investigating the sizes and morphologies of
redshift 4 < z < 8 galaxies in the CANDELS GOODS-S, HUDF and HUDF parallel
fields. Based on non-parametric measurements and incorporating a careful
treatment of measurement biases, we quantify the typical size of galaxies at
each redshift as the peak of the log-normal size distribution, rather than the
arithmetic mean size. Parameterizing the evolution of galaxy half-light radius
as $r_{50} \propto (1+z)^n$, we find $n = -0.20 \pm 0.26$ at bright
UV-luminosities ($0.3L_{*(z=3)} < L < L_*$) and $n = -0.47 \pm 0.62$ at faint
luminosities ($0.12L_* < L < 0.3L_*$). Furthermore, simulations based on
artificially redshifting our z~4 galaxy sample show that we cannot reject the
null hypothesis of no size evolution. We show that this result is caused by a
combination of the size-dependent completeness of high-redshift galaxy samples
and the underestimation of the sizes of the largest galaxies at a given epoch.
To explore the evolution of galaxy morphology we first compare asymmetry
measurements to those from a large sample of simulated single S\'ersic
profiles, in order to robustly categorise galaxies as either `smooth' or
`disturbed'. Comparing the disturbed fraction amongst bright ($M_{UV} \leq
-20$) galaxies at each redshift to that obtained by artificially redshifting
our z~4 galaxy sample, while carefully matching the size and UV-luminosity
distributions, we find no clear evidence for evolution in galaxy morphology
over the redshift interval 4 < z < 8. Therefore, based on our results, a bright
($M_{UV} \leq -20$) galaxy at z~6 is no more likely to be measured as
`disturbed' than a comparable galaxy at z~4, given the current observational
constraints.
