HST/WFC3-IR Imaging of Exceptionally Luminous Himiko/CR7-Like Galaxies at z>6

Physical processes governing the formation/evolution of high-redshift galaxies in the epoch of reionization (EoR; z>6) are still not well understood. In most cases, EoR galaxies are fuzzy faint blobs showing little internal structure, and fitting various theoretical models to spatially-integrated spectral energy distributions (SEDs) is often all that can be done. There are, however, a small number of luminous EoR galaxies, such as Himiko at z=6.595 and CR7 at z=6.601, whose exceptional brightnesses have allowed spatially-resolved studies and have revealed some fascinating details.

Although such luminous EoR galaxies are rare, the Subary/Hyper Suprime-Cam (HSC) survey has recently discovered 7 comparably bright EoR galaxies with y < 25 mag (in comparison, y=25.4 and 24.5 mag with Himiko and CR7, respectively). Here, we propose to obtain HST/WFC3 near-infrared images for these exceptionally luminous z>6 galaxies with the F105W, F125W, and F160W filters. Our goals are, (1) to identify the rest-frame UV continuum morphology, (2) to measure UV continuum spectral slopes, and (3) to compare the UV continuum morphology with those of Ly-alpha, [C II], and dust emission when possible. The obtained HST data will allow us to probe the internal structures and underlying physical processes in these remarkable high-redshift galaxies.

The targeted z>6 EoR galaxies are so bright that they will also make excellent targets for NIRSpec IFU observations, enabling us to study the internal structure and kinematics of these high-redshift galaxies in greater detail. The obtained HST data will also be essential to make effective us of precious JWST time.