R. J. Bouwens, P. A. Oesch, G. D. Illingworth, I. Labbe, D. Magee, R. Smit, M. Franx, P. G. van Dokkum, M. Trenti, V. Gonzalez, C. M. Carollo
Ultra-deep WFC3/IR observations on the Hubble Ultra Deep Field from the HUDF09 program revealed just one probable z~10 candidate UDFj-39546284. UDFj-39546284 had all the properties one might expect of a galaxy at z~10. Not only did the candidate show no detection in any ultra-deep imaging data blueward of the F160W band, but the candidate exhibited a very blue spectral slope redward of the break, showing no prominent detection in the IRAC observations. The chief concern about this candidate was that it was a 5.9sigma single-band detection and therefore had a small chance of being spurious. Using new, deep WFC3/IR F160W observations over the HUDF09/XDF field, we test the reality of this candidate. We find that UDFj-39546284 is detected at 4.3sigma in the new observations, and at 7.1sigma in the full 77-orbit H_160-band image. This demonstrates at >99.99% confidence that this z~10 candidate corresponds to a real source. We strengthen the z~10 candidate detection even further by taking advantage of an even deeper stack of optical XDF observations over the HUDF and with 120-hour IRAC IUDF10 observations to place even tighter constraints on its probable redshift. For flat priors, we find that the source is 97% likely to be at redshift greater than 8. The full H_160-band stack also provides information on the morphology of the source. The source appears to consist of a bright core embedded in a larger structure extending to 0.4" (1.6 kpc physical).
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http://arxiv.org/abs/1211.3105
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