HST Follow-up Observations of Two Bright z ∼ 8 Candidate Galaxies from the BoRG Pure-parallel Survey

Abstract

Abstract We present follow-up imaging of two bright (L > L*) galaxy candidates at z ≳ 8 from the Brightest of Reionizing Galaxies (BoRG) survey with the F098M filter on the Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3). The F098M filter provides an additional constraint on the flux blueward of the spectral break, and the observations are designed to discriminate between low- and high-z photometric redshift solutions for these galaxies. Our results confirm one galaxy, BoRG_0116+1425_747, as a highly probable z ∼ 8 source, but reveal that BoRG_0116+1425_630—previously the brightest known z > 8 candidate (m AB = 24.5)—is likely to be a z ∼ 2 interloper. As this source was substantially brighter than any other z > 8 candidate, removing it from the sample has a significant impact on the derived UV luminosity function in this epoch. We show that while previous BoRG results favored a shallow power-law decline in the bright end of the luminosity function prior to reionization, there is now no evidence for departure from a Schechter function form and therefore no evidence for a difference in galaxy formation processes before and after reionization.