Color-selected Galaxies at z 6 in the Great Observatories Origins Deep Survey

We report early results on galaxies at z~6, selected from Hubble SpaceTelescope imaging for the Great Observatories Origins Deep Survey. Spectroscopyof one object with the Advanced Camera for Surveys grism and from the Keck andVLT observatories a shows a strong continuum break and asymmetric lineemission, identified as Lya at z=5.83. We detect only five spatially extended,z~6 candidates with signal-to-noise ratios > 10, two of which havespectroscopic confirmation. This is many fewer than would be expected ifgalaxies at z=6 had the same luminosity function as those at z=3. There aremany fainter candidates, but we expect substantial contamination fromforeground interlopers and spurious detections. Our best estimates favor a z=6galaxy population with fainter luminosities, higher space density, and similarco-moving ultraviolet emissivity to that at z=3, but this depends critically oncounts at fluxes fainter than those reliably probed by the current data.