@article {28046,
	title = {Galaxies at z~7-8: z850-Dropouts in the Hubble Ultra Deep Field},
	journal = {The Astrophysical Journal Letters},
	volume = {616},
	year = {2004},
	note = {n/a},
	month = {December 1, 2004},
	pages = {L79-L82},
	abstract = {We have detected likely z~7-8 galaxies in the144{\textquoteright}{\textquoteright}{\texttimes}144{\textquoteright}{\textquoteright} Near-Infrared Camera andMulti-Object Spectrometer (NICMOS) observations of the Hubble Ultra DeepField. Objects are required to be \&gt;=3 σ detections in bothNICMOS bands, J110 and H160. The selectioncriteria for this sample are(z850-J110)AB\&gt;0.8,(z850-J110)AB\&gt;0.66(J110-H160)AB+0.8,(J110-H160)AB\&lt;1.2 and no detectionat less than 8500 {\r A}. The five selected sources have totalmagnitudes H160,AB~27. Four of the five sources are quiteblue compared to typical lower redshift dropout galaxies and areclustered within a 1 arcmin2 region. Because all five sourcesare near the limit of the NICMOS data, we have carefully evaluated theirreality. Each of the candidates is visible in different splits of thedata and a median stack. We analyzed several noise images and estimatethe number of spurious sources to be 1+/-1. A search using anindependent reduction of this same data set clearly revealed three ofthe five candidates and weakly detected a fourth candidate, suggestingthat the contamination could be higher. For comparison with predictionsfrom lower redshift samples, we take a conservative approach and adoptfour z~7-8 galaxies as our sample. With the same detection criteria onsimulated data sets, assuming no evolution from z~3.8, we predict 10sources at z~7-8, or 14 if we use a more realistic (1+z)-1size scaling. We estimate that the rest-frame continuum UV (~1800{\r A}) luminosity density at z~7.5 (integrated down to0.3L*z=3) is just0.20+0.12-0.08 times that found at z~3.8 (or0.20+0.23-0.12 times this quantity includingcosmic variance). Effectively this sets an upper limit on the luminositydensity down to 0.3L*z=3 and is consistent withsignificant evolution at the bright end of the luminosity function fromz~7.5 to 3.8. Even with the lower UV luminosity density at z~7.5, itappears that galaxies could still play an important role in reionizationat these redshifts, although definitive measurements remain to be made.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555.
},
	url = {http://adsabs.harvard.edu/abs/2004ApJ...616L..79B},
	author = {Bouwens, R. J. and Thompson, R. I. and Illingworth, G. D. and Franx, M. and van Dokkum, P. G. and Fan, X. and Dickinson, M. E. and Eisenstein, D. J. and Rieke, M. J.}
}
