P. A. Oesch, R. J. Bouwens, G. D. Illingworth, V. Gonzalez, M. Trenti, P. G. van Dokkum, M. Franx, I. Labbe, C. M. Carollo, D. Magee
We present new z~8 galaxy candidates from a search over ~95 arcmin^2 of
WFC3/IR data. These are used to determine the bright end of the UV luminosity
function (LF) of star-forming galaxies at z~8. Our analysis is based on newly
acquired WFC3/IR imaging data obtained as part of the CANDELS Multi-Cycle
Treasury program over the GOODS South field, which allows us to triple the
search area for bright z~8 galaxies in the GOODS South. These new data are
combined with existing deep optical ACS imaging to search for relatively bright
(M_UV<-19.5 mag) z~8 galaxy candidates using the Lyman Break technique. To
minimize contamination from lower redshift galaxies, we make full use of all
optical data and impose strict non-detection criteria based on an optical
chi^2_opt flux measurement. In the whole search area we identify 11 candidate
z~8 galaxies, spanning a magnitude range H_160,AB =25.8-27.5 mag. The new data
show that the UV LF is a factor ~2 lower at M_UV < -19.5 mag than previously
determined. Combining this new sample with the previous candidates from the
HUDF09 and ERS data allows us to perform the most accurate measurement of the
z~8 UV LF yet. Schechter function fits to the combined data result in a
best-fit characteristic magnitude of M_*(z=8) = -19.80+-0.52 mag. The faint-end
slope is very steep, though quite uncertain, with alpha=-2.06+-0.41. A
combination of wide area data with additional ultra-deep imaging will be
required to significantly reduce the uncertainties on these parameters in the
future.
View original:
http://arxiv.org/abs/1201.0755
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