Physical Properties of Spectroscopically-Confirmed Galaxies at z >= 6.
  II. Morphology of the Rest-Frame UV Continuum and Lyman-alpha Emission
  We present a detailed structural and morphological study of a large sample of
spectroscopically-confirmed galaxies at z >= 6, using deep HST near-IR
broad-band images and Subaru optical narrow-band images. The galaxy sample
consists of 51 Lyman-alpha emitters (LAEs) at z ~ 5.7, 6.5, and 7.0, and 16
Lyman-break galaxies (LBGs) at 5.9 < z < 6.5. These galaxies exhibit a wide
range of rest-frame UV continuum morphology in the HST images, from compact
features to multiple component systems. The fraction of merging/interacting
galaxies reaches 40% ~ 50% at the brightest end of M_1500 <= -20.5 mag. The
intrinsic half-light radii r_{hl,in}, after correction for PSF broadening, are
roughly between r_{hl,in} ~ 0.05" (0.3 kpc) and 0.3" (1.7 kpc) at M_1500 <=
-19.5 mag. The median r_{hl,in} value is 0.16" (~0.9 kpc). This is consistent
with the sizes of bright LAEs and LBGs at z >= 6 in previous studies. In
addition, more luminous galaxies tend to have larger sizes, exhibiting a weak
size-luminosity relation r_{hl,in} \propto L^{0.14} at M_1500 <= -19.5 mag. The
slope of 0.14 is significantly flatter than those in fainter LBG samples. We
discuss the morphology of z >= 6 galaxies with nonparametric methods, including
the CAS system and the Gini and M_20 parameters, and demonstrate their validity
through simulations. We search for extended Lyman-alpha emission halos around
LAEs at z ~ 5.7 and 6.5, by stacking a number of narrow-band images. We do not
find evidence of extended halos predicted by cosmological simulations. Such
Lyman-alpha halos, if they exist, could be weaker than predicted. Finally, we
investigate any positional misalignment between UV continuum and Lyman-alpha
emission in LAEs. While the two positions are generally consistent, several
merging galaxies show significant positional differences. This is likely caused
by a disturbed ISM distribution due to merging activity.
