Star formation at z ∼ 6: The hubble ultra deep parallel fields

R. J. Bouwens, G. D. Illingworth, R. I. Thompson, J. P. Blakeslee, M. E. Dickinson, T. J. Broadhurst, D. J. Eisenstein, X. Fan, M. Franx, G. Meurer, P. Van Dokkum

Research output: Contribution to journalArticlepeer-review

102 Scopus citations


We report on the i-dropouts detected in two exceptionally deep Advanced Camera for Surveys fields (B435, V606, i775, and z850 with 10 σ limits of 28.8, 29.0, 28.5, and 27.8, respectively) taken in parallel with the Ultra Deep Field Near-Infrared Camera and Multi-Object Spectrometer observations. Using an i-z > 1.4 cut, we find 30 i-dropouts over 21 arcmin2 down to z850, AB = 28.1, or 1.4 i-dropouts arcmin-2, with significant field-to-field variation (as expected from cosmic variance). This extends i-dropout searches some ∼0.9 mag further down the luminosity function than was possible in the Great Observatories Origins Deep Survey (GOODS) fields, yielding a ∼7 times increase in surface density. An estimate of the size evolution for UV-bright objects is obtained by comparing the composite radial flux profile of the bright i-dropouts (z850, AB < 27.2) with scaled versions of the Hubble Deep Field-North and -South U-dropouts. The best fit is found with a (1 + z)-1.57 +0.50 -0.53 scaling in size (for fixed luminosity), extending lower redshift (1 < z < 5) trends to z ∼ 6. Adopting this scaling and the brighter i-dropouts from both GOODS fields, we make incompleteness estimates and construct a z ∼ 6 luminosity function (LF) in the rest-frame continuum UV (∼1350 Å) over a 3.5 mag baseline, finding a shape consistent with that found at lower redshift. To evaluate the evolution in the LF from z ∼ 3.8, we make comparisons against different scalings of a lower redshift B-dropout sample. Although a strong degeneracy is found between luminosity and density evolution, our best-fit model scales as (1 + z) -2.8 in number and (1 + z)0.1 in luminosity, suggesting a rest-frame continuum UV luminosity density at z ∼ 6 that is just 0.38 -0.07+0.09 times that at z ∼ 3.8. Our inclusion of the size evolution makes the present estimate lower than previous z ∼ 6 estimates.

Original languageEnglish (US)
Pages (from-to)L25-L28
JournalAstrophysical Journal
Issue number1 II
StatePublished - May 1 2004


  • Galaxies: evolution
  • Galaxies: high-redshift
  • Galaxies: luminosity function, mass function

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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