EVOLUTION OF THE SIZES OF GALAXIES OVER 7 < z < 12 REVEALED BY THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN
- Institute for Cosmic Ray Research, The University of Tokyo, Kashiwa 277-8582 (Japan)
- Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ (United Kingdom)
- Department of Astrophysics, California Institute of Technology, MS 249-17, Pasadena, CA 91125 (United States)
- Department of Astronomy and Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
- Space Telescope Science Institute, Baltimore, MD 21218 (United States)
- UPMC-CNRS, UMR7095, Institut d'Astrophysique, F-75014 Paris (France)
- Department of Astronomy, Graduate School of Science, The University of Tokyo, Tokyo 113-0033 (Japan)
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) {sup s}, we obtain a best-fit index of s=-1.30{sup +0.12}{sub -0.14} 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 0.05-1.0 L{sub z=3}. 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.
- OSTI ID:
- 22270541
- Journal Information:
- Astrophysical Journal, Vol. 777, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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