Steven L. Finkelstein, Russell E. Ryan, Casey Papovich, Mark Dickinson, Mimi Song, Rachel S. Somerville, Henry C. Ferguson, Brett Salmon, Mauro Giavalisco, Anton M. Koekemoer, Matthew L.N. Ashby, Peter Behroozi, Marco Castellano, James S. Dunlop, Sandy M. Faber, Giovanni G. Fazio, Adriano Fontana, Norman A. Grogin, Nimish Hathi, Jason JaacksDale D. Kocevski, Rachael Livermore, Ross J. McLure, Emiliano Merlin, Bahram Mobasher, Jeffrey A. Newman, Marc Rafelski, Vithal Tilvi, S. P. Willner

Research output: Contribution to journalArticlepeer-review

516 Scopus citations


We present a robust measurement and analysis of the rest-frame ultraviolet (UV) luminosity functions at z = 4-8. We use deep Hubble Space Telescope imaging over the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey/GOODS fields, the Hubble Ultra Deep Field, and the Hubble Frontier Field deep parallel observations near the Abell 2744 and MACS J0416.1-2403 clusters. The combination of these surveys provides an effective volume of 0.6-1.2 × 106 Mpc3 over this epoch, allowing us to perform a robust search for faint (MUV = -18) and bright (MUV < -21) high-redshift galaxies. We select candidate galaxies using a well-tested photometric redshift technique with careful screening of contaminants, finding a sample of 7446 candidate galaxies at 3.5 < z < 8.5, with >1000 galaxies at z ≈ 6-8. We measure both a stepwise luminosity function for candidate galaxies in our redshift samples, and a Schechter function, using a Markov Chain Monte Carlo analysis to measure robust uncertainties. At the faint end, our UV luminosity functions agree with previous studies, yet we find a higher abundance of UV-bright candidate galaxies at z ≥ 6. Our best-fit value of the characteristic magnitude is consistent with -21 at z ≥ 5, which is different than that inferred based on previous trends at lower redshift, and brighter at ∼2σ significance than previous measures at z = 6 and 7. At z = 8, a single power law provides an equally good fit to the UV luminosity function, while at z = 6 and 7 an exponential cutoff at the bright end is moderately preferred. We compare our luminosity functions to semi-analytical models, and find that the lack of evolution in M∗UV is consistent with models where the impact of dust attenuation on the bright end of the luminosity function decreases at higher redshift, although a decreasing impact of feedback may also be possible. We measure the evolution of the cosmic star-formation rate (SFR) density by integrating our observed luminosity functions to MUV = -17, correcting for dust attenuation, and find that the SFR density declines proportionally to (1 + z)-4.3±0.5 at z > 4, which is consistent with observations at z ≥ 9. Our observed luminosity functions are consistent with a reionization history that starts at z ≳ 10, completes at z > 6, and reaches a midpoint (xHII = 0.5) at 6.7 < z < 9.4. Finally, using a constant cumulative number density selection and an empirically derived rising star-formation history, our observations predict that the abundance of bright z = 9 galaxies is likely higher than previous constraints, although consistent with recent estimates of bright z ∼ 10 galaxies.

Original languageEnglish (US)
Article number71
JournalAstrophysical Journal
Issue number1
StatePublished - Sep 1 2015
Externally publishedYes


  • Early universe
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift
  • Ultraviolet: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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