The Bright-end Galaxy Candidates at z ∼ 9 from 79 Independent HST Fields

November 2018 • 2018ApJ...867..150M

Authors • Morishita, T. • Trenti, M. • Stiavelli, M. • Bradley, L. D. • Coe, D. • Oesch, P. A. • Mason, C. A. • Bridge, J. S. • Holwerda, B. W. • Livermore, R. C. • Salmon, B. • Schmidt, K. B. • Shull, J. M. • Treu, T.

Abstract • 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 ({M}_UV}∼ -22.6+/- 0.3 mag), making it one of the brightest candidates at z> 8 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, {M}_UV}^*=-{21.0}_-1.4^+0.7 mag, and {log}{φ }^*=-{4.2}_-0.9^+0.6 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.

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Takahiro Morishita

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