Evolution of the sizes of galaxies over 7 < z < 12 revealed by the 2012 Hubble ultra deep field campaign

Yoshiaki Ono, Masami Ouchi, Emma Curtis-Lake, Matthew A. Schenker, Richard S. Ellis, Ross J. McLure, James S. Dunlop, Brant E. Robertson, Anton M. Koekemoer, Rebecca A.A. Bowler, Alexander B. Rogers, Evan Schneider, Stephane Charlot, Daniel P. Stark, Kazuhiro Shimasaku, Steven R. Furlanetto, Michele Cirasuolo

Research output: Contribution to journalArticlepeer-review

120 Scopus citations


We analyze the redshift- and luminosity-dependent sizes of dropout galaxy candidates in the redshift range z ∼ 7-12 using deep images from the 2012 Hubble Ultra Deep Field (UDF12) campaign, which offers two advantages over that used in earlier work. First, we utilize the increased signal-to-noise ratio offered by the UDF12 imaging to provide improved measurements for known galaxies at z ≃ 6.5-8 in the HUDF. Second, because the UDF12 data have allowed the construction of the first robust galaxy sample in the HUDF at z > 8, we have been able to extend the measurement of average galaxy size out to higher redshifts. Restricting our measurements to sources detected at >15σ, we confirm earlier indications that the average half-light radii of z ∼ 7-12 galaxies are extremely small, 0.3-0.4 kpc, comparable to the sizes of giant molecular associations in local star-forming galaxies. We also confirm that there is a clear trend of decreasing half-light radius with increasing redshift, and provide the first evidence that this trend continues beyond z ≃ 8. Modeling the evolution of the average half-light radius as a power law, (1 + z)s, we obtain a best-fit index of over z ∼ 4-12. A clear size-luminosity relation is evident in our dropout samples. This relation can be interpreted in terms of a constant surface density of star formation over a range in luminosity of . The average star formation surface density in dropout galaxies is 2-3 orders of magnitude lower than that found in extreme starburst galaxies, but is comparable to that seen today in the centers of normal disk galaxies.

Original languageEnglish (US)
Article number155
JournalAstrophysical Journal
Issue number2
StatePublished - Nov 10 2013


  • galaxies: evolution
  • galaxies: formation
  • galaxies: high-redshift
  • galaxies: structure

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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