Physical properties of spectroscopically confirmed galaxies at z ≥ 6. II. Morphology of the rest-frame UV continuum and Lyα emission

We present a detailed structural and morphological study of a large sample of spectroscopically confirmed galaxies at z ≥ 6 using deep Hubble Space Telescope (HST) near-IR broad-band images and Subaru Telescope optical narrow-band images. The galaxy sample consists of 51 Lyα 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 correcting for point-spread function (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 found in previous studies. In addition, more luminous galaxies tend to be larger and exhibit a weak size-luminosity relation, r _hl, in∝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 concentration, asymmetry, and smoothness system and the Gini and M ₂₀ parameters, and demonstrate their validity through simulations. We search for extended Lyα 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 Lyα halos predicted by cosmological simulations. Such halos, if they exist, could be weaker than predicted. Finally, we investigate positional misalignment between the UV continuum and Lyα emissions in LAEs. While the two positions are generally consistent, several merging galaxies show significant positional differences. This is likely caused by a disturbed interstellar medium distribution due to merging activity.