Аннотация
We present our results on an extended search for z~10 galaxies over ~160
arcmin^2 of WFC3/IR data in the Chandra Deep Field South. These public data
sets are from the HUDF09, ERS, and CANDELS surveys, and reach to 5 sigma depths
ranging from 26.9 to 29.4 in H_160 AB mag. z>~9.5 galaxy candidates are
identified via J_125-H_160>1.2 colors, and non-detections in any band blueward
of J_125. Spitzer IRAC photometry is key for separating the genuine high-z
candidates from intermediate redshift (z~2-4) galaxies with evolved or heavily
dust obscured stellar populations. After removing 15 sources of intermediate
brightness (H_160=24-26 mag) with strong IRAC detections, we only find one
plausible z~10 galaxy candidate in the whole data set, previously reported in
Bouwens et al. (2011). However, the present data set is much larger than before
and covers a 3x larger area. This allows us to set much stronger limits on the
evolution of the UV luminosity function (LF). If the evolution of the z~4-8 LFs
is extrapolated to z~10, six z~10 galaxies are expected in our data. The
detection of only one source suggests that the UV LF evolves at an accelerated
rate before z~8. The luminosity density above our survey limit is found to
increase by a factor 7-25 in only 170 Myr from z~10 to z~8. This increase is
>=2.5x larger than expected from the lower redshift extrapolation of the UV LF.
Thus we are likely witnessing the first rapid build-up of galaxies in the heart
of cosmic reionization. Future deep HST WFC3/IR data, reaching to well beyond
29 mag, will be essential for a more robust quantification of this accelerated
evolution based on the detection of larger samples of z~10 candidates reaching
below L*.
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