Evolution of the Sizes of Galaxies over 7<z<12 Revealed by the 2012 Hubble Ultra Deep Field Campaign
A paper on "Evolution of the Sizes of Galaxies over 7<z<12 Revealed by the 2012 Hubble Ultra Deep Field Campaign" has been submitted to the Astrophysical Journal. A preprint is available at http://www.arxiv.org/abs/1212.3869:
Evolution of the Sizes of Galaxies over 7<z<12 Revealed by the 2012 Hubble Ultra Deep Field Campaign
Authors:
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
Abstract:
We analyze the redshift- and luminosity-dependent sizes of dropout galaxy candidates in the redshift range z~7-12 using deep images from the UDF12 campaign, data which offers two distinct advantages over that used in earlier work. Firstly, we utilize the increased S/N ratio offered by the UDF12 imaging to provide improved size measurements for known galaxies at z=6.5-8 in the HUDF. Specifically, we stack the new deep F140W image with the existing F125W data in order to provide improved measurements of the half-light radii of z-dropouts. Similarly we stack this image with the new deep UDF12 F160W image to obtain new size measurements for a sample of Y-dropouts. Secondly, 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 significantly higher redshifts. Restricting our size measurements to sources which are now detected at >15sigma, 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 s=-1.28+/-0.13 over the redshift range z~4-12, mid-way between the physically expected evolution for baryons embedded in dark halos of constant mass (s=-1) and constant velocity (s=-1.5). A clear size-luminosity relation, such as that found at lower redshift, is also evident in both our z- and Y-dropout sample. This relation can be interpreted in terms of a constant surface density of star formation over a range in luminosity of 0.05-1.0L*_z=3.(abridged)
The Hubble Ultra Deep Field 2012 program is a collaboration between the California Institute of Technology, the University of Arizona, the University of Edinburgh, the Space Telescope Science Institute, the University of California Los Angeles, the University of Tokyo, and the Institut Astrophysique de Paris. Support for this Program was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research In Astronomy, Incorporated, under NASA contract NAS5-26555.
