SuperBoRG: Search for the Brightest of Reionizing Galaxies and Quasars in HST Parallel Imaging Data

The Hubble Space Telescope (HST) has been providing tremendous survey efficiency via its pure-parallel mode by observing another field in parallel with the primary instrument in operation for the primary observation. In this study, we present a new archival project, SuperBoRG, which aims at compiling data taken in extragalactic parallel programs of HST with the Wide Field Camera 3 in the past decade, including pure-parallel (BoRG, HIPPIES, and COS-GTO) and coordinated-parallel (CLASH and RELICS) programs. The total effective area reaches ∼0.41 deg² from 4.1 Ms, or 47 days, of observing time, which is the largest collection of optical-to-near-infrared imaging data of HST for extragalactic science. We reduce all data in a consistent manner with an updated version of our data reduction pipeline, including a new sky background subtraction step. When available, imaging data from the Spitzer Space Telescope are also included in photometric analyses. The data set consists of 316 independent sight lines and is highly effective for identification of high-z luminous sources (M _UV ≲ −20 mag) at z ∼ 7–12, helping to minimize the effects of cosmic variance. As a demonstration, we present three new z ≳ 7 source candidates, including one luminous galaxy candidate at z _phot ∼ 10.4 with M _UV ∼ −21.9 mag; the best-fit spectral energy distribution implies a large amount of stellar mass ($log{M}_{\ast }/M_{\odot }$ ∼ 10) and moderate dust attenuation (A _V ∼ 1.4 mag), though the possibility of it being a low-z interloper cannot be completely rejected (∼23%) with the current data set. The data set presented in this study is also suited for intermediate- and low-z science cases.