Physics and Astronomy
We present a full data analysis of the pure-parallel Hubble Space Telescope (HST) imaging observations in the Brightest of Reionizing Galaxies Survey (BoRG[z9]) in Cycle 22. The medium-deep exposures with five HST/WFC3IR+UVIS filter bands from 79 independent sightlines (∼370 arcmin2) provide the least biased determination of number density for z 9 bright galaxies against cosmic variance. After a strict two-step selection for candidate galaxies, including dropout color and photometric redshift analyses, and revision of previous BoRG candidates, we identify one source at z ∼ 10 and two sources at z ∼ 9. The z ∼ 10 candidate shows evidence of line-of-sight lens magnification (μ ∼ 1.5), yet it appears surprisingly luminous (MUV ∼ -22.6 ± 0.3 mag), making it one of the brightest candidates at known (∼0.3 mag brighter than the z = 8.68 galaxy EGSY8p7, spectroscopically confirmed by Zitrin and collaborators). For z ∼ 9 candidates, we include previous data points at fainter magnitudes and find that the data are well fitted by a Schechter luminosity function with α = -2.1-0.3+0.3, MUV∗ = -21.0-1.4+0.7 mag, and Mpc-3 mag-1, for the first time without fixing any parameters. The inferred cosmic star formation rate density is consistent with unaccelerated evolution from lower redshift.
Morishita, T.; Trenti, M.; Stiavelli, M.; Bradley, L. D.; Coe, D.; Oesch, P. A.; Mason, C. A.; Bridge, J. S.; Holwerda, Benne W.; Livermore, R. C.; Salmon, B.; Schmidt, K. B.; Shull, J. M.; and Treu, T., "The Bright-end Galaxy Candidates at z ∼ 9 from 79 Independent HST Fields" (2018). Faculty Scholarship. 495.