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 M_UV<-20.5 mag, suggesting hierarchical build-up of the brightest galaxies at high redshift. We use half-light radius to describe the galaxy sizes, and find that the intrinsic radii r_hl,in, after correction for PSF broadening, are roughly between 0.05" and 0.3", with a median value of 0.13" (~0.75 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 physical sizes, exhibiting a size-luminosity relation r_hl,in ∝ L^0.2. The slope 0.2 is significantly flatter than those in previous fainter LBG samples. We for the first time characterize the morphology of z>6 galaxies using nonparametric methods, including the CAS system, the Gini and M_20 parameters. Compared to low-redshift galaxies, our galaxies appear in slightly different locations in the parameter space, mainly due to their small sizes in the HST images. However, we find strong correlations between the measured parameters, as expected from their definitions. This implies that these nonparametric methods could be still applicable for z>=6 galaxies, if used with caution. 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. [abridged].